The Premier League 2 will become an under-21 competition instead of under-23 from next season.
The change was partly to match the age limits of the EFL Trophy - where some Premier League clubs field under-21 teams - and international competitions.
The average age of players in the Premier League 2 is 19.
Clubs will be allowed to use five overage outfield players and one goalkeeper - up from the previous limit of three and one respectively.
Manchester City have won the past two titles.