It is very okay since cartoons such as SpongeBob SquarePants are a way through which people relax and thus they do not have an age limit even though they are more popular with children. SpongeBob SquarePants is a cartoon that anyone can laugh through.
Spongebob has some stupidly messed up episodes. The one where they make silly faces and they get stuck that way is nothing short of creepy. If I wasn't an adult watching that I might have had nightmares.
Spongebob FTW!! You're never too old for a sponge in square pants. And anyways, I keep finding it funnier the older I get (the old episodes in particular). It takes a special kind of adult to love Spongebob ;D