This is everything that is wrong with summer tournaments.
My son was born in March of 2001 and plays on a 2019 team for the summer. According to this bracket methodology, he could play on a 2021 team. That is all well and good except the fact that he is 5'7 and weighs 160 pounds.
What happens in these tournaments? Parents accuse the bigger kids of driving their parents to/from the events, smaller kids (who are age appropriate) get chippy with the larger kids and the pre-puberty kids react and chaos ensues. It is a recipe for disaster, but no one seems to care.
Bottom line is US Lacrosse needs to take a page out of the NCYFL book and go to picture i.d. cards and end this nonsense once and for all. I know it will never happen but one can dream.
How can your kid born in 2001 play 2021 based on the stated age rules? He plays 2019, which is correct if he is in 7th grade. What are you seeing here that leads you to believe he can play 2021? Your math is wrong by a lot. Even if he failed a grade twice, he could still not play in this particular tourney as a 2021 because the age rules prevent that from happening.
