Alice's mom was around twenty in the early 60s; she used to go to clubs to see James Jones (a thinly disguised David Bowie) when he was starting out. (This is a plot point in Year One, before Four Doctors, as Jones also travels with the Doctor and Alice.) When Year One starts, Alice's mother has just died in 2014, and we're shown that she looks quite old. While I don't think we've ever learned Alice's birth year, her mother's age puts Alice's age in her early 40s. She's an interesting contrast to the eleventh Doctor; he's all mania and exuberance, and she's depressive and weighted down by it all. They really do care about each other.