On the surface this looks like a good idea and I'm not opposed to it but it does bring up the following questions:
I assume this would mean no day 31 builds for anyone in GLB, not just players that are being signed to PeeWee teams. So there would have to be a season cut-off date after which no players could be created, agents would probably have to wait until after play-offs are done, or day 41, to start creating new players? Would this turn off some new owners just coming into the game who find out they can't create a new player for a couple of weeks?
If no new builds were allowed until day 41 would that give owners who every season create new players enough time to build their 5000 flex points of players? Won't it be harder on the servers if all new players being built are now concentrated into a tighter time period?
Maybe leave the build date open and on day 1 of the regular season, every player who is signed to a PeeWee team has their XP automatically go to 900 at level 1.