14 is the right age. If your 14 as a soph. Then you'd graduate hs at 16 and go to college at 17
He's going into 8th grade, not 9th grade and he is ALREADY 14.
He will be 18 before he starts his senior year of high school, and depending on his birthday, might be 19 before he graduates.
The difference a year makes early in your teens is huge, and a lot of people who dominate pee wee do nothing later on because their advantage was that they developed early.
Hell, when I was 11 (6th grade) we played football against a kid who was about 6'4" 200+ lbs who was our age. He pretty much did whatever the hell he wanted during the game and physically dominated everyone on our roster.
Fast forward and 3 different kids on my pee wee team ended up playing D-1 Football (for OU, Tulsa, and OK ST).
That kid did NOTHING.