I've always said that if you're too old for cartoons, you're too old. To paraphrase C.S. Lewis "When I became an adult, I put away childish things, and that includes the fear of being seen as childish." He was talking about why he thought it was okay for adults to read fairy tales, but it applies just as well to cartoons, videogames, and pretty much anything that brings joy both to children and adults. Also OP, someone seriously made fun of you for watching Phineas and Ferb? That show is the best thing to come out of the Disney Channel since Dave the Barbarian, which in turn was the best thing to come out of it since Ducktales, Tailspin and the rest of that block got cancelled.
[sub]I'll be 21 in under a month, by the way, so I'm legally an adult, but still qualify as a kid to those who are significantly older than me, or at least a kid of the college variety.[/sub]