Spongebob is 24 years old.I'm not sure how long he has been on TV though...Like i said,He's 24 but he acts like a kid.Examples: Jellyfishing, Playing with Patrick, And laughing a lot. Here's a funny pic!
Yes, the "driver's license" said 1986. But he made a krabby patty perfectly when he was a baby, and had a krabby patty both when he was still a baby and before he was born. His birthday and Christmas were shown several times (often in the same season) on different dates. And when he forgot to tie his shoe, he was shown with his current legs inside an egg. Before Spongebob, Jim was the fry-cook, but there was a different fry-cook when he moved next to Squidward, and already knew Patrick. So, according to the series, he might have several birthdays. But if you go by the sereis itself, he's about 13-14 years old from 1999-2012.
According to what I've heard Spongebob is currently 26 years of age. In the episode where Spongebob goes into people's dreams, he has a dream where he gets his license. On his license, his birth year is 1986 which would make him 26, 27 this year depending on the month and day.
Spongebob was born 7/11/1986, meaning he is 27 this 2013, as shown on his dream license in sleepy time. In the same episode, Mr. Krabs' license is shown and was born 11/30/1942, meaning he is 71 this 2013.