From US Lacrosse website: 2015 Age Grouping Quick Reference Table
Birthdate Age Bracket
Born on or after 9/1/1999 U15
Born on or after 9/1/2001 U13
Born on or after 9/1/2003 U11
Born on or after 9/1/2005 U9
....So, to take this a step further and fill in for U14, U12, U10 & U8, we assume 9/1 is the cut-off date for each given year.
September 1 is also the academic cut-off date for "most" states (to correct a previous poster), so this is reasonable.
The way I see it, we all need to pressure not only US Lacrosse, but also our local town/county & state officials to set these standards.
We need to be vocal and enlist the support of coaches and parents.
It's been said before, if soccer/hockey, etc. can do it, than so can lacrosse.
Get involved, be persistent, make this happen.