Actually I believe that the idea that Humans could not have children with Twi'leks was originally from the X-Wing novels and Traviss just used it. Frankly I think the EU saying the two species couldn't have kids was a bad idea no matter who came up with it though.
Oh, I was just pointing out that the Clone Commando series used the idea as a minor plot point. I'm not sure where it came from originally, but you're probably correct. (I need to re-read the X-Wing series... it's been too long.) That said, I respectfully disagree that it was a bad idea, but to list my reasons would likely derail the thread.
Regarding clones and aging, the Clone/Imperial Commando series (the later novels, especially) are a decent resource for a game that centered around the clones and their accelerated aging process.