What I love about Jack in Torchwood is that he really feels immortal and very old. Like, with other old/immortal characters in other series/movies, you don't get that feeling. They behave like someone of the age they look like. A classic is young vampire who is 200 years old but still hangs out with teenagers. Even if there are adults around, a 50 year old will still be 150 years younger and writers forget what it is to be old. Sometimes they give them the nostalgia of "all my family has died" but that is it.
Jack is joyful and playful, still gets nervous about daily life things like asking someone out (even if he flirts a lot, with almost anyone, including "older" people) but he doesn't talk about certain things (and every time you feel it is because it pains him or because he has spoken about it once and again to many different people just not this time). He knows humanity back and forth. He has been killed several times and still he has hopes and enjoys whatever joys the world can bring him. And to me that is what makes him feel as old as he is. He has accepted he will live forever and whoever he will like will disappear, but he will like them and enjoy their company as long as they want him. He doesn't push too much, doesn't expect too much but is still there, giving chances. What makes him old is not wise sentences or mysterious vibes. What makes him old is the patience and the melancholy in his every movement while still enjoying what life offers.
