Your doctor may be able to estimate how long a wait you have in store for you. By looking at your son's height compared to other family members and examining the bone growth plates, it's possible to get an idea if it's a matter of months or years.
It is best to wait to have an ACL repair until the bone growth is complete. There are some other treatment options. Doctors at the University of Texas describe "physes-sparing" ACL repairs. The physis is the growth plate at the end of the bone. An ACL repair usually drills holes through bone that may still be growing in children and some teens. Any disruption of the physis can cause permanent damage.
The physes-sparing operation passes a graft through the joint without drilling a hole in the bone. There are some problems and difficulties with this procedure. Most doctors prefer to wait until the bone has stopped growing to repair the damaged ligament.
Once you know how long you might have to wait (remember, it's just an educated guess), then speak with the football coach about the situation. Find out what your options are before planning treatment.