Well, it just depends on how you see things. It all goes back to St. Nicholas, who's feast day is celebrated on December 6th (the day he died in 343). It's not altogether clear when he was born. So I've always said that Santa was born when St. Nick died in order to carry on his tradition. So by that measure, Santa will be 1,669 years old this year. Your source is obviously measuring from his approximate birth date, which was in 270 (or thereabouts).