It's not just that he was a little bit older. It's how his body developed. He walked into junior hockey a man.
The 2017-18 Oceanic roster lists him at 6'2", 196:
Rimouski Oceanic roster in the 2017-2018 QMJHL season. Player birthdate, birthplace, height and weight information for the Rimouski Oceanic.
www.quanthockey.com
The Rangers list him right now at 6'1", 194:
The official 2024 - 2025 roster of the New York Rangers, including position, height, weight, date of birth, age, and birth place.
www.nhl.com
We'll call it 6'1" and a half. Point is, he had the body he has now at 16 and he was playing against kids.
Compare that to Kevin Hayes who was drafted at 6'2" and made his NHL debut at 6'5". Or K'Andre Miller who was 6'2" at
Minnetonka High and has to be close to 6'6" now.
It's not age, it's when you grew and when you had an adult body. Getting your adult body early skews your early numbers.
Granted, Larry Bird was 6'9" when he was like 11, but that's Larry Bird. He was an exception in every way.