I don't know if to call them dumb stuff or not, but there's plenty of childish things that I enjoy, and I'm 23...
Fairly Oddparents, Billy and Mandy, Johnny Bravo, Cow and Chicken...
Also, some anime like Moetan, Mayoi Neko Overrun, Renkyuun San Magical Pokaan...
And of course, old movies like Dumb and Dumber, Liar Liar, The Naked Gun trilogy...
I could name a lot, lot of things