Not hold-backs. You have your dates wrong. Here are the facts.
From US Lacrosse Website. The new rules state:
DOB
Born 9/1/2002 through 8/31/2003
Age Group
15U
Grade Affiliation
9th
HS Graduation Yr.
2021
So if you are born before 9/1/2003, such as 1/25/2003, you are supposed to be on 2021.
The original poster should have stated 9/1/2002 which would make you a 2020.