Greetings, all fellow players.

One rule question that I can't quite understand/find in the rulebook: Is it possible for my character to buy talents or skills on the rank that is lower than my character's current rank?

Like, My character is currently rank 3 now, and have some experience points. However, there are some skills and/or talents on rank 1 section that I find useful (EX: Astartes Weapon Specialization). But I'm not rank 1 now. Can I still buy that talent?

Have a nice day.

I don't have the rulebook in front of me so I can't back this up with a page reference but yes, I think it's possible to buy from lower levels. The logic behind this is that otherwise it's entirely possible for a marine to level up to the next rank before he has taken all the skills and traits he wants from the previous rank which would cause them to miss out on something important (like a skill advancement that locks them out of the +10 and +20 skills or a talent which is a prerequisite for other talents). Also, spending XP on attribute boosts would be unduly onerous since it would preclude you from buying one or even several skills and talents in that level.

All in all, from a logical perspective as well as a gameplay perspective, I would definitely allow it.

"You may buy Advances from any Rank Advancement Scheme you currently hold or have previously held"

(Page 57 "Ranks")

It's definitely allowed.

If it wasn't possible, it would severely limit your advances aqusitions, and would probably paint you into a corner, mayhaps not even being able to buy relevant things to reach the next rank. So yeah, being able to buy advancements from previous ranks is rather important.