You don't need to be 18 to enter the jam! Anyone is welcome to enter the game jam and submit any project they wish. (Excepting for the family friendly part - I'd appreciate if all submissions followed that requirement.)
However, in order to be eligible to win a prize, you do need to be 18 years or older. If you would like to submit a game and excuse yourself from compensation for any reason (such as being under 18), please state "I excuse myself from compensation" anywhere on your game's itch.io page. Please don't try and cheat the rules. No good things come from cheating. 馃檪
As for why that is, there are many legal / tax / ethical / social reasons why I don't think it's a good idea to encourage financial competition between minors and adults. If you're under 18 and want to make video games - that's awesome! I'm more than happy to help you on your game dev journey, feel free to join in the fun of the jam! I just can't pay for you it yet.
