The competition is usually for U-23s, but the world football governing body has made the change, following the postponement of the Games.
It would ensure players who were eligible for the Tokyo Olympics this summer, will still be able to take part next year.
Any player born on or after January 1, 1997, will be able to play, alongside three allocated over-aged players.
The men’s tournament will kick off before the July 23, 2021 opening ceremony.
The women’s event has no age limit The Fédération Internationale de Football Association said.
FIFA has also called off all men’s and women’s national team games set to be played in June 2020, as the coronavirus pandemic continues to spread.