NOTABLE ITEMS IN USA LACROSSE'S PLAYER SEGMENTATION POLICY:

An emphasis on grouping players by single-age years (12-month span), with exceptions of up to 24 months for age groupings as needed. (Note: NLF has chosen to use 15-month age groupings for its clubs and events.)
A September 1 birthdate is the start of new age groupings in an attempt to align with the majority of school systems nationwide to allow players to play with people in their own grade level when possible.
Firmly defined playing season that begins its 12-month cycle on September 1.
Standardized nomenclature that lists maximum age first (i.e., 12U, not U12).