Gunning a kid at age 7?!!?
What's going on in today's society?
Enjoy watching the kid play the game at that age regardless if he throws 48 mph or 8 mph. Focus on making sure he's having fun rather then making sure he's throwing hard enough.
A lot can happen by the time he enters High School, heck a lot can happen by the time he's 10.
Why the curiosity on the velo of 7 year old?