Not really true, especially for defensemen. More late bloomers make it at defense than kids considered top players at Freshmen and Sophomores in high school. Part of it is a size issue but usually it's the kids who keep working at their game and don't get showered with 'can't miss' accolades.
Says the dad of a kid who never saw D-I varsity ice until his senior season and then 10 months later made a top USHL team while all the heavily touted kids in the region went on to play Club hockey.
Check your notes, a 'stud' 14 year old defensemen rarely makes it.