User blog comment:Adventuretimegurl123/OH MY!! HUGE ADVENTURE TIME NEWS!! :D/@comment-67.224.131.57-20120818163310/@comment-5800078-20120818191802

Well he started off 12, then mid-Season 2 he turned 13 and around late Season 3 he turned 14. So he'll turn 15 by Late Season 4/Early Season 5 by the current rate, and will age further into age 16 by Season 6.