Here's some information that I think many don't realize in this thread:

From USALacrosse website:
2015 Age Grouping
Born on or after 9/1/2005 is U9

This decision is not random or redshirting, the majority of states in the US have cutoffs in August through Sep 1 for kindegarten, including Maryland. Therefore, if you are at a travel tournament or eventually play college level, your child will always play against children in this age range. Therefore, it would actually hurt your child if lacrosse in NY used a December cutoff because they would not have the same level of experience in play that everyone else in the country is having in the same grade level/graduating class. New [lacrosse] is a fact, one of only a handful of states with December as the cutoff for public schools, most NY independent private day and boarding schools have a September 1 cutoff.
Here are the kindergarten cutoffs by state:
Alabama- September 1
Alaska- August 15

Arizona- September 1

Arkansas-September 15

California-October 1(2013-14) September 1(2014 onwards)

Colorado- September 15

Connecticut-October 1

Delaware - August 31

Florida-September 1

Georgia- September 1

Hawaii-December 31

Idaho- September 1

Illinois-September 1

Indiana- August 1

Iowa- September 15

Kansas-August 31

Kentucky-October 1

Louisiana- September 30

Maine-October 15

Maryland-September 1

Massachusetts-September 1

Michigan-November 1(2013-14), October 1(2014-15), September 1(2015 onwards)

Minnesota-September 1

Mississippi-September 1

Missouri-August 1

Montana- Sept 10

Nebraska-October 15

Nevada-September 30

New Hampshire-September 30

New Jersey-October 1 and later (choice left to school district)

New Mexico - September 1

New [lacrosse]-December 1

North Carolina-October 16

North Dakota- August 1

Ohio-August 1 or Septemer 30(choice left to school district boards)

Oklahoma- September 1

Oregon-September 1

Pennsylvania - Choice left to local school district

Rhode Island- September 1

South Carolina- September 1

South Dakota - September 1

Tennessee - August 31

Texas-September 1

Utah-August 31

Vermont-August 31 - Dec 31 (Choice left to local school district)

Virginia-September 30

Washington- August 31

West Virginia- September 1

Wisconsin-September 1

Wyoming - September 15