Just the answer: You can join regardless of your age. The rules don’t state anything about age. “The only rule we have is that your game must not include any NSFW and offensive/discriminatory content.” - states the jam overview. I think you should read it if you haven’t.
Extra: Your age has almost nothing to do with game development at all. Sometimes a Kid can be smarter than an adult, and also an adult being smarter than kids is considered normal and is normal as well. It depends on the person, not their age. (Sorry for bad English though, I hope you at least understood what I mean)