One key factor....it's generally acknowledged by most national federations that among MEN, other than the very rare MH's HK's AP's, etc. they may have pushed athletes too hard, too young. And today, they sport is even more brutal in a physical sense than it was. There is good reason why Norway defunded their B team, and send SO many kids to the USA and the NCAA. Race NCAA, race a full NorAm schedule, fly home for the occasional EC or WC starts. Grow up, grow bigger, grow stronger. Graduate at 23 or so, and THEN go after it. However if you are on a differ trajectory, like Norwegian Atle McGrath {Felix's son}, you are going to be brought to the EC and WC sooner.
So....it sort of "all depends." Lots of studies about this over the years. most recently the one commissioned by Dan Leever for the USSA/USST. General theme.....don't push team too fast. Which is a big change form 15-20 years ago with the USST.