a 13 year old CAN own a gun...but not an MP-7.
I get that you are new to this but if you are interested in firearms, I suggest you buy a book or read a bunch online about the different types and what is available to you where you live.
YOU must be 18 to purchase a long gun, 21 for a handgun/class III weapon. However, you only need to be 12 to own a firearm. If your dad feels you are responsible enough, he can buy a firearm and give it to you as a gift.