* His job: SpongeBob works at the Krusty Krab, which suggests he's old enough to be employed. This implies he's at least 16 years old, the legal working age in most places.
* His behavior: SpongeBob often exhibits childish behavior, which could point to him being younger than a typical adult.
* His appearance: SpongeBob's appearance hasn't changed much over the years, suggesting he doesn't age at a typical human rate. This leaves his age open to interpretation.
In conclusion: While no official age is given, based on clues from the show, SpongeBob is likely somewhere between 16 and 20 years old. However, it's important to remember that he's a cartoon character, and his age is ultimately up to the creators' interpretation.