My son has a birthday after the May 1 deadline. I had him start playing grade appropriate starting in 7th grade. This was despite being an undersized physical late bloomer compared to other Majors level travel players and a lot of his teammates. He was 5’2” 100 in 13u and 5’4” 120 in 14u. I didn’t want him entering high school coming off one year on the 60/90 competing in 13u slo mo (relative to 14u) ball.
Once you believe your kid can compete he should play up as far as possible. He played 16u as a 14u eligible the summer after freshman year. I saw 16u as the equivalent to varsity ball without the the 17u studs. He showed he was ready for varsity ball. His high school coach didn’t want freshmen on varsity. He was starting to grow.
He was 5’11” 135 in 16u. Academy coaches saw something in him. He was invited to be on 17u teams post soph summer. He was 6’ 160 by soph season. The metrics were now visible. He was ready to show.
Despite both kids (daughter played softball) being physical late bloomers with late birthdays I never gave it a thought. Age and birth date could only be an excuse if allowed to be. I knew they would catch up physically. I’m 6’1” and the second shortest male on both sides. My (ex) wife is 5’8”. While my son was a 5’ 90 12yo his five years older sister was 5’10”.
Until my son had his growth burst he was very conscious of being the short kid. Especially in basketball. One time when he was a 5’2” 13yo we walked by a 6’4” guy who didn’t look coordinated just walking. My son muttered, “What a waste of freak’n height!” He did grow to be 6’2”.