Also in early days of MLS, they dealt with a smilar lawsuit over restrictions of player movement the person/group lost cause there are alternates to Soccer than MLS. Like there are alternates pro leagues than just NHL/AHL/ECHL.
To add. about the age 20 requirement issue for AHL etc, I think the reason why such a restriction is in place has to do with are you mature physically, emotionally and mentally enough as a person to handle players that are older and stronger/bigger than you.
Even if this person suing was drafted by a NHL player is he mature enough to handle players that are way older than him and possible bigger in weight and size. If he isn't mature enough to be on a NHL roster why would he necessary be mature enough a ECHL or a AHL roster.