I think Kiefer has said this is his last go around as Jack Bauer, as he feels he's getting up there in years (not to mention Jack, who I think I read is now 57).
47, actually. He was born in December of 1966.
Ignoring the "perpetual now" notion by the show's creators and actually accounting for the time that's passed between seasons, 24 is about two or three years ahead of us, putting Jack probably in his early 50s. And that's assuming the first season took place in the then past of 2000, an election year, rather than in the then future of 2004, the next presidential election year. (And ignoring the silly notion it took place in the hen present of 2001, not even a mid-term election year.)
There's a lot of fluidity in how we can look at the timeline of 24 since nothing has really been nailed down, and even on-screen references like dates on phones and documents isn't consistent. The true date is never explicitly stated, the closest we get is in the first season taking place on the day of the California Presidential Primary which usually takes place in March, though it can shift around quite a bit, the times of the sunrise and sunset in Day 1 also suggest a late winter/near equinox time setting.
The next closest we get is probably in Season 3 which takes place during the first Presidential debate, usually taking place in September.
Of course, we know the *exact* date for "Redemption" which takes place on Inauguration Day which is on or around January 20, depending on whether or not that date falls on a weekend.
(Which, in Taylor's case it would have, ergo, Redemption takes place on January 21, 2013.)
The current season, again assuming S1 takes place in 2000 and ignoring the "perpetual now" notion, is some time in 2018, making Jack 52.
