Besides the heeling of the bone you also have to take the atrophy into account. A 4 week cast is not too long and being 16 it will probably not be too bad, but you will only know for sure when you get the cast off and test the mobility and strength of your arm.
After I broke my wrist (complex fracture) I needed a cast for 3 months and after that the atrophy was horrible as I was only able to apply 1 pound of pressure with that hand. I tried going out after 2 weeks, but wasn't able to apply enough pressure to steer the kite so it wasn't safe and had to wait a couple weeks more before slowly getting back to my old self again.
Thanks for the recommendation i hope i can get back out quick and after do you put anything in your wrist when riding? Thanks