Couple of problems here.
The French did not say he was a sniper, only a good shot. The sniper tag was added here on FR.
The guy is only a 2LT so he hasn't been in the service too long. Doubt he has advanced training in much of anything.
The Military school he was enrolled in only takes those born in France. He might still be Muslim, France and Spain are full of them, but he must be native born.
I got my first bb gun at 8 years, pellet gun at 10, .22 at 12, 12 gauge at 14, .30/06 at 16 and person at 19 from 700 yds. Age has nothing to do with it.