No one is getting weaker, slower, and less coordinated as they age from 13 to 15. Testosterone is a super drug, and it's flowing like a river at this age. The same kid will always be better at 15 than he was at 13. That's a fact. To admit this isn't taking away from anyone's hard work and dedication. But to deny it is silly.
Yes, this is obviously true. That's why we don't have age limits ands weight classes, because they totally don't matter.
If you want numbers, count how many 4th, 5th, 6th, 7th and 8th graders place at middle school states each year.
When you buy a coffee at McDonald's, it has a warning that the contents inside are hot. They do this because some moron burned there mouth and then sued McDonalds, as though they didn't realize the coffee would be hot. In a sane world, McDonalds wouldn't have to put this on their cups. That's how I feel about the rule that you have to be 19 to participate in high school sports. In a sane world, this wouldn't have to be stated, it would be obviously understood. But alas, we have to put it in the rule book because teams would be rolling out 21 year olds and people on this forum would be saying "rules are rules, age doesn't matter, you're just a sore loser!"