Great news, congratulations to your son.
The Varsity asst at our HS told me that when Junior was a freshman, the coaches had him slated to be cut as a soph and not make the soph team. He had a good fall showing and made the soph starting rotation.
At varsity as a Junior, he couldn't get a varsity start.
As a senior, he set most of the school pitching records.
Now as a junior at college, his pitching coach refers to him as the leader of the staff in front of the team.
From being a late bloomer myself, to a worrying parent later, the one lesson I always pounded into my kids heads...The world is not ordered as you see it today, it will change, you need to work to be part of the positive change.
Tell him to continue to work hard and good things will continue to come.