Rules for 16-17 might be some some minor changes for 17-18
https://ussoccer.box.com/s/ddh3x0fztgwufv8x1bc3dep1i97t0q5h
2003 & 2004: 16 min, 20 max but only 18 on the game day roster
2002,01: combined min of 32, combined max of 46, but only 18 on the game day roster per team
00,99: combined min of 32, combined max of 46, but only 18 on the game day roster per team
"Each roster shall be published on the official U.S. Soccer Development Academy registration website, and shall be considered the official roster of the Academy club. There is a minimum of 32 full-time (FT) players per Academy club combined in the U-15/16 and U-17/18 age group and 16 full-time players each in both the U-13 & U-14 age groups. There is a maximum of 20 full-time players at both the U-13 & U-14 age groups and 46 full-time players combined between the U-15/16 and U-17/18 age groups. At the U-12 age group, there may be between 24-26 full-time players. There is no limit to the number of rostered players that do not have United States citizenship.
Only 11 players on the field and 3 sub movements plus half time so typically half the bench may get into games depending on the situations.