What does the size and weight have to be for a Junior League bat?

By Juniors, I assume that's 13-14 year olds. If so, your bat can't be more than 34 inches long (you'll probably want a 31 or 32 inch length, weight between 21-24 ounces. The main thing is that it can't have a barrel diameter of more than 2 5/8". Used to be 2 3/4" but that changed last year. So the diameter is that of a high school bat, but Juniors aren't required to be -3 (drop 3). If you're a big strong kid, then try to go -5, like a 32/27 or 31/26, it will help transition you to the high school size.

Go to your local baseball store (not the big boxes like Academy or Sports Authority...their personnel are clueless). Find the locally owned baseball specialty store and ask those guys, they'll steer you to the right size for you.