NYCFC just signed a 14 year old homegrown player, and he's playing on NYCFC's U17 team.
I'm thinking the rules with MLS Next are different than they were with USSDA.
EDIT: I stand corrected:
"Players that have participated or are participating in any college program at any level (Division I, Junior College, etc.) are not permitted to participate in any MLS NEXT Events unless the MLS NEXT Club seeking to register such a Player is granted approval by PDev following Clubs submission of an MLS NEXT Player Reinstatement Form. As further described in the MLS NEXT Player Reinstatement Form, examples in which PDev may allow such Players to participate in MLS NEXT include, but are not limited to, the following: An MLS NEXT age-eligible Player who is under a professional contract with an MLS NEXT Clubs professional Affiliate.
Well, this is a huge win for player development!