Good god, you guys went mad here yesterday while I was busy and overnight while I was asleep!!!!!
Okay, thoughts. I'm not very good at this extrapolation stuff so people to bounce ideas off are very welcome!
Age: Jack will be approaching his bicentennial, which might be a thing that gets him thinking about stuff. If he's been stuck here for 20 years already, he'll already have had some big bouts of depression about the fact that being stuck here 'forever' means a lot longer for him than it does for mortals, whose real, physical bodies are presumably still ageing and who will therefore presumably die eventually while he won't.
Physically, he won't have aged much at all and will still look thirty-something, beyond the odd grey hair or two, so a lot of other people will have aged past him, which may have been a sore point with some of them.
Would almost certainly be performing some kind of leadership role. Because I'm lazy, I'm going to say that's some kind of position on Kitty's council. :-)
And if I'm going for that I may as well go for the rest of her idea, i.e. no more wardens, which means NO MORE SEX BANDS. Which means that casual sex is go again and in 20 years, even if he's still with Ianto and Spike and mostly staying faithful to them, there would almost certainly have been breaks in which he slept around any of the rest of the dome who would have him. So feel free to assume your character was one of them and leave me a comment to say so! :-D