Message from US Soccer Federation
Here is a video that explains the what and why for the birth year changes and rule changes that are being mandated from the USSF.
Birth Year Change Information

As some of you are aware, the USSF instituted a few major changes to youth soccer which took affect in the 2016 season. The two main category changes that impacted all youth soccer clubs in the nation are:

1) The age group adjustment, moving from the current academic year to a calendar year requirement(see age chart below).

2) The adjustment in the competitive format for the micro/mod (U6-U12) players.

We will continue to allow players to request to play up, but players cannot play down. We are sensitive to the fact that teams will want to stay intact, especially those D2 (U13-U19) teams.