Today, British autistic savant Daniel Tammet is 10,220 days, or 245,280 hours old (that's 28 years for you non-savants out there). He is blessed/cursed with the kind of savantism made famous by Dustin Hoffman in Rain Man (formerly known as "idiot" savantism), but Daniel manages to sustain relatively normal social interaction with others. (He credits growing up in a family of nine children, and thus being forced to socialize, for his normalcy relative to other savants, of which there are only about 50 known in the world.)
A lot of savants can do things that no normal person can do, like tell you what day of the week August 18, 1876 was without consulting an almanac, in about five seconds (it was a Friday), multiply 27 to the power of four in his head (531,441) or memorize and recite long strings of numbers with ease. But there are a few things he can do that even most savants cannot. For instance, he once learned functional Icelandic in a week, and recited pi to several thousand places from memory (without errors -- it took more than five hours).
So how does he do it? As a recent profile of Daniel on 60 Minutes revealed, the answer may shed light on the abilities of all savants: he is a synesthetic. That is to say, he associates numbers with colors, just as composer Franz Liszt claimed to have associated music with color. (Hip-hop artist Pharrell Williams also claims to have synesthesia.)
Interesting note: one man who has done some crucial research in this area is Oxford professor of developmental psychopathology Simon Baron-Cohen, cousin of Borat star Sascha Baron-Cohen.