This definitely needs to be implemented but, id prefer it not only to be extended to Goalies but, for it to be age capped and not games played capped.
AI Teams go after older players to fill these leagues entirely too much.
Maybe instead of age or games played restrictions the Veteran Rule for HLM is a Team can have 3 forwards, 2 Dmen and 1 goalie that have reached peak (grey) status for the Development Leagues. This way teams pushing for playoffs or a deep run can still have some helpful guys ready to go in case of injury but, not have a negative impact on the development of youth players.
I think its important to tweak the rule for HLM vs the In Real Life rule for the Users that are not running a bunch of leagues because a lot of the Veteran Players would still qualify for the Development Leagues due to them not getting games in the Major leagues meaning the AI teams would still be able to sign all Veteran/Older players to their development leagues.
This add could potentially be one fix for Users who like to do long sims. The game has a issue with not producing the right amount of quality players long term. Upping Draft Quality doesnt do enough to counter it since the Drafted players typically are not getting ice time in the development leagues due to the AI going after older players instead of developing the youthful ones.
Upping Development is not a fix either because it impacts every player.