One is never too old to see animated films! I saw Ponyo this past weekend, and it was what I thought it would be: cuteness, laughter, bright colors in every scene, good animation, and more.
There is something about the colors in the movie that made it very enjoyable to me; the characters had a traditional solid-appearance, but the backgrounds were like color pencil/pastel paintings. I consider that one of the most special features of the film.
I don't think I'll ever get tired of watching animated movies; I saw Up recently and it made me cry 10 minutes into the movie! The next one I plan to watch will probably be The Princess and The Frog. It was about time Disney released a movie like that again! Too much 3d lately :P