I really wish we would all follow the USA Lacrosse age guidelines. But it has to start with the clubs - because the clubs control the tournaments.

The following age groupings are determined as of the August 31
st
preceding competition
.
NOTE: Age group references used in this section are in common usage but should not be understood literally. The
U15 (read: “Under 15”) grouping means
that, if a player is 14 years old on the cutoff date, he may participate in U15
competition as a 15
-
year old.
U15:
All players must be 14 years old or younger on the August 31
st
preceding competition. It is recommended
that when multiple teams exist wi
thin a program, the program should consider physical size, skill, and
maturity when organizing teams.
U13:
All players must be 12 years old or younger on the August 31
st
preceding competition. It is recommended
that when multiple teams exist within a pr
ogram, the program should consider physical size, skill, and
maturity when organizing teams.
U11:
All players must be 10 years old or younger on the August 31
st
preceding competition. It is recommended
that when multiple teams exist within a program, th
e program should consider physical size, skill, and
maturity when organizing teams.
U9:
All players must be 8 years old or younger on the August 31
st
preceding competition. It is recommended that
when multiple teams exist within a program, teams shoul
d consider physical size, skill, and maturity.

reference - http://www.uslacrosse.org/Portals/0/pdf/boys-youth-rules.pdf