There is nothing to stop. Physical maturity is a major benefit, plain and simple. Just accept it and admit it.(No my kid is not young for his grade, he's old for the grade and his birth date is within the district cut off of his grade. Yes, his size and strength are a benefit.)
For anyone to say that a kid whose born in 1998 and is playing 2018 has no advantage over a 2000 kid, that is just plain stupidity.
Think a couple of years ahead. Why do you think most 10th graders can't compete/start at the HS varsity level? (some can)Stick skills? No, physical maturity!! Unless he's 17 yrs old and in 10th grade. Which is what the 1998 kid playing 2018 will be in 10th grade!
On a higher level. Why do you think a school like Deerfield is so highly ranked in the high school arena? Because northern Mass is a new Hot Bed? No, because they have a boat load of 13th graders playing HS lacrosse.
The only way we will weed out these people who think there's no difference is to go by birth certificate. Plain and simple. Notice it's always the parents of the kid whose older that thinks it's "OK". If two kids are within the same age bracket and one matures earlier, then that's just the luck of the draw. If one is almost a year and a half to two years older and they're playing in the same "GRADE" then that's an unfair advantage. Some might go so far as to call it something else! We'll let people decide what to call it on their own.