Just look at the age difference. Assume everyone is playing correct age. I.E. 9 and 10 year olds playing.
an ASA age 9 born in December versus an ASA person born in January. Buy May the 9 year old is 9 years 6 months, but the 10 year old is actually 11 years 5 months old. That's an extreme but a 23 month difference.
It's even worse in the fall. Our first tournament a couple of years ago we were a 10 U team playing our first 12U tournament. We played a 2nd year 12U team that chose not to move up in our first game. It looked like a bunch of high school players on the other team.