I was going to say he looks too old, but then realized that I have been to busy to watch the show and have had stopped in the end of the second season (while watching what I can of newer episodes), and Finn is the only cartoon character, to my knowledge, to age with his show, both literally and figuratively. For as Finn slowly matures to remove the gauze of childish naivete and sees further into the the war-worn husk of the world that was once a world that he lives in, so do we go through the same as the visions of Ooo are served to us each season in more and more confused, emotionally dark and/or disturbing content and subject matter. He is about sixteen for his sixth season, I assume (where I am, he is still tweleve-ish.) Children grow up so fast, don't they? (I hope that the show continues long enough to see what they possibly have for us in Finn's adulthood.)