In the original teams, older players weren't necessarily more skilled than younger players. It was like they had been playing playground Buzzer Beater when the professional leagues were formed and hadn't really had professional training.
This is only the 3rd season for NT. When the teams first started, a player with a 6K salary was considered a potential candidate for the team. In selecting players, most NT gave preference to younger players since they had more long time potential, and were just as good. In addition, BB increased the training rate for younger players in order to boost skills more towards their more mature levels.
It will be interesting to see the effect of the newly introduced potential. All the old players have All Star potential. In the long term someone with All Star potential might simply not be able to develop into a NT player. There appears to be some correlation between initial skills and potential, but it is not absolute. In my league's draft, there was a player with Announcer potential who had a higher salary and presumably higher skills, than another player who had MVP potential.
When the U21(?) teams are introduced, player selection will be interesting since the best players might not be the best players when they are 25, even with the same training.