I was sort of tempted to discuss the types of good choices for who a Rogue Trader might want to breed with, but the options are as many, and varied, as the types of people who bear the Warrants of Trade, so I think I'll go this way, instead, on the silly question train:

At what age should a Rogue Trader start planning to have a family?

So, most Warrants are hereditary; you got yours from your Mother, Father, maybe an Aunt, Uncle, or Grandparent. In much the same way, you need to have an heir to inherit it from you, someday. They need time to learn the ways of the vocation, if you will, but not so long as to need to get rid of you, before their own glory years are used up, as Warrants often seem to pass only when the current bearer dies, or becomes incapacitated. If I drew a parallel from real life aristocracy, I could see starting to pop out children almost immediately, since you never know what tomorrow holds, for you (assassination?), or for them (illness?), but then, in 40k, these types of people can live for so much longer, if their wealth, and luck, holds out. The books have rich RTs spending their wealth on rejuv treatments that make a 150-year old look like they are 40, and some people can live to be 200, a few even pushing 300 years (the Venerable Cal), before even the AdMech's science starts to run out of ways to prolong your life. If you had a child in your 30's, and lived to be 200, they'd already be 160+, before they got the Warrant, likely parents, themselves, and maybe even grandparents, and that seems weird, except for needing the time to learn all the stuff you need to be a Rogue Trader/captain of a ship. I think they describe Aoife Armengarde as around 150, while her daughter, Igraine, sounds like she's, maybe, in her 20-30s, so are the available breeding years likewise extended? Would it seem "normal" to have a child at 100, in RT? How many years "training" should it take, assuming you aren't newly minted, or got your Warrant in a card game?

How old are people, in 40k, when they decide to have children, assuming they have access to the life-extending procedures of rejuvenants? How have these numbers worked out for players, assuming you've done due diligence, in game, to see to your dynasty's future? Sorry for the weird question, but in my writing, the main leads are often referred to as "the Young Bloods", by the older, more powerful representatives of power, in Koronus, as they are in their 30s, and holding Warrant, while your Armengardes, Fels, and many other established Rogue Traders seem to be sitting in their 100+s. I have trouble imagining if the late Lord Qel-Drake, or Lady Artymus, had their heirs when they were 20, or 120. One of those weird twists of fiction.

The answer would be : depends of your dynasty, the way the Warrant is transmitted, and the current state of the lineage.

For instance, in the french campaign I've mastered, the RT was in her forties, yet she went immediateley to look for a wedding in game, in order to have heirs in short order. She got some of her genetical material safeguarded in iscreet places, should something happen to her. She married on Scintilla downward volontariliy to someone of good fortune yet not a peer, to be sure to keep him under her control. All of this because she was the last of her line.

it was a good idea of sake-keeping as she became sterile after a cybernetic ressruection thanks to warp-tainted poisonning. Less so when a rival manage to find one of such cache, and use it to create five thousands copies of her in order to sell them as cheap prostitues as an insult on Footfall...

Anyway; considering the existence of vat-grown babies, cryo-tubes, one could conceive an heir very soon, kept them frozen and put them out of the ice when deemed suitable for instance. Of course, you have to ensure they are kept safe, not pulled out of cryo-stasde too late or too early. Too much potential heirs is as much trouble as not enough for a noble lineage.

Basicallty, this is a great question of concern of any RT worth his gelt, full of potential drama and plot twist, considering any device they use to try to safeguard their line.

Indeed. Equally, remember that the warrant is not necessarily "goes to the next one down the generational chain".

Having a 'next generation' early(ish) on is not a stupid idea, because a rogue trader who leads his or her expeditions in person is in a risky trade.

But you might want to have children at a 'normal' age - give or take a decade or so - but on the understanding that the warrant will go to their children, or even their grandchildren, not to them. it still gives them a stake in "the good of the dynasty" but avoids the situation you often see with (as an example) the Catholic Papacy - where the office tends to pass from the elderly to the elderly, and instead allows you to have extended periods of continuity under the same warrant-holder.

As far as I'm aware, juvenat essentially extends all biological processes. So certainly it would be possible (or at least not out of character) for a rejuvenated individual to have children in their 150s or so.

Less so when a rival manage to find one of such cache, and use it to create five thousands copies of her in order to sell them as cheap prostitues as an insult on Footfall...

I would think they would reproduce in a similar fashion to modern day royalty, assuming the Warrant is hereditary. Which is to say, have a small pack of children as soon as you find someone of a suitable social standing/wealth/genetic compatibility/whatever under the theory that at least half of them will be wastrels, and of the half that aren't, most will die or turn away from the dynasty due to one form of treachery or another.

I had an RT that would actually seek volunteers, and screened the entire populations of a few discovered worlds looking for the best genetic matches, and I would spend a single point of PF for 16 game years and at the end he would get the PF back, along with an heir. After a while (like 80 game years), he had a company-sized unit of dynastic heirs serving as uberstormtroopers, but he was a strict Trader Militant, so it made sense to test the potential heirs in combat.

The only restriction on someone of an RT's resources is the desire to reproduce. It is something I ask every player when they start, as most simply don't even consider it when playing Grimdark Space Pirate.

Think nobility. A Rogue Trader would have 2 considerations...

1. Eugenics - genetically advantaged offspring such that they are better suited to "taking" wealth, power and title.

2. Power/Gain - marrying for money, property, title, connections, etc... so your children inherit not only your wealth, but their other parent's as well.

That is all.

Most of this makes sense; it's just weird to imagine having a "kid" need to wait over a century, before they have any good opportunity to succeed you. Granted, they will have rejuvenant treatments, too, so they might not seem 100+ years old, but it's just sort of difficult to wrap my brain around.

Remember that not all or even most of your descendants will directly inherit your Warrant; depending on how long you live and when you inherited it, it may be a more reasonable assumption that the most promising of your grandchildren or great grandchildren to be the heritor. The 40k galaxy is immensely dangerous at the best of times, and there are numerous examples in the fluff of lines ending or being bequeathed on far flung distant relations due to the rate of attrition and uncertainty with warp travel and communication. In the Enforcer series, the Warrant to be passed winds up in the hands of a minor noble on a backwater world, the result of an illicit liaison by a Rogue Trader passing through. Even with a double handful of children and grandchildren, picking the best of the survivors will likely be a crapshoot. I think you would be best served to draw a clear line of succession and seal it with a blood signature, with addenda ejecting from consideration anyone who starts offing family members.

Viper brings up a couple of points I forgot, namely that the warrant need not pass to direct family. The Warrant of Trade is less linear than some seem to be taking it; it may be held by an individual, but the realities of managing a dynasty requires many hands. Perhaps the immediate offspring of the warrant holder are immersed in some form of politics or obligations that excludes them from holding the Warrant, or perhaps they were in succession, but the choice was not approved by the High Lords, so the next candidate is considered. Without a clear, regulated line of succession, the person that ends up holding the Warrant is the victor by dint of luck as much as any other characteristic. The age of the holder is not of any concern; I would think that an individual would not be seriously considered for a high level government position without being at least a century old. What does it matter that the heir watched their parent hold the warrant for a century or more before it came to their hands? what does it matter if the holder has five generations of family younger than themselves? Feudal kings rarely inherited the crown peacefully at any age under 40, which was already pushing the life expectancy of medieval times. This age/perception of experience would be even more pronounced in 40k: "Who is this guy telling us what to do? He has got to be a quarter the age of the last guy in charge! Where are his bionics? Does he know what he is doing?"

There are quite a few points to consider:

- On the RP side offspring is too often neglected. It is one of the basest of human drives that player characters almost never seem to exhibit. Understandable from the gaming point of view, but if you truly go in character this question should be adressed. All living humans are confronted in one way or another with this problem and so should all characters.

- Once you have this question of offspring popping up, the next question appears: What are your hopes for your offspring? Do you as a Rogue Trader wish to see them following in your path of glory and derring do?

- After which we can enter into a more rational field of power and politics. What is your Warrant of Trade? What is its goal? And what are your goals? If you are a true paragon of the Imperium only interested in increasing the Rule of Man, you will look quite differently at your heirs than you would as a potentate hoping to carve out its own dominion in the lawless expanse. Same goes for the rules under which the Warrant was granted. Is it to pass through direct descendance? Can you choose amongst your descendants? Can you adopt? And who choses and confirms said heir? Endless permutations of all the above are possible.

- Age, oh yes, quite rightly, age, with all the rejuvenat posibilities that might get akward. But I think that a bit of age would be wise on a Rogue Trader, certainly considering the fact that the wisdom conferred by experience is not diminished by the increasing decrepitude of old age in WH40K (at least for those with the means and up to a certain extent).

- Combining all of this I would as a Rogue Trader choose to adopt by heir from my wider offspring, a bit comparable to the adopted Emperors in Rome. This gives you a very good shot at getting the best one of the flock. But the obvious problem is infighting. Or do I see a perfect start of a RT campaign appearing....

I'll say that the RT in my campaign developed something of a Harem, being the last survivor of the line.

I was sort of tempted to discuss the types of good choices for who a Rogue Trader might want to breed with, but the options are as many, and varied, as the types of people who bear the Warrants of Trade, so I think I'll go this way, instead, on the silly question train:

At what age should a Rogue Trader start planning to have a family?

So, most Warrants are hereditary; you got yours from your Mother, Father, maybe an Aunt, Uncle, or Grandparent. In much the same way, you need to have an heir to inherit it from you, someday. They need time to learn the ways of the vocation, if you will, but not so long as to need to get rid of you, before their own glory years are used up, as Warrants often seem to pass only when the current bearer dies, or becomes incapacitated.

<sigh> "What does a ten-thousand-year-old dragon do?"

Should mostly depend on the dynasty - traditions and political situations vary. IIRC some are watching their nominal head, too.

Those who let the Sisters Fabulous arrange their less interesting affairs probably are susceptible to their matchmaking projects, otherwise mostly random.