But hey top teams training 18yo again, the world is wonderfull.
Something that would help is being there for new managers and encouraging them to train up 18 year olds well. The bigger the supply of well trained 18 -21 year olds that come through the more that will be available for the top teams at affordable prices to train onwards...
High league teams do train young players (even under 20). It's more rare than in low leagues, but for two reasons:1) Low leagues cannot keep training players over 22 years old if they have been well trained before, cause of high salaries.2) High leagues need to have at least one player with skills of a 22 y old guy to be competitive. Like in NBA, team need experimented players to play the big games.
As for a D-League team, how can you imagine someone willing to use a player who had an half training. Even more a team in high league. There, we need players who have been trained 98% of the time, not 45% of the time.