Cut off date in my town is Oct 1st.
My daughter with an Oct birthday just missed it, so she's one of the oldest in her class. My son with a September birthday made it, but he wasn't ready, everyone who met him-his own teachers and friends who are teachers told me to hold him back. Nice! LOLThey were 100% spot on though.
So he's held back, but he's less than 2 month younger than his sister was in K, so it seems normal to us to start K at almost 6 now.
I have met only a few kids who were held back, all were boys and not one was held back for sports or size-I don't get that-how do you even know if your son will want to play sports anyway?
As for being 19 when you graduate HS, my husband was, and he started school on time, with a June birthday, would have just turned 18 before high school graduation, but got left back in 1st grade so he graduated high school at 19.
Didn't seem to hurt him much, successful, college educated, good career-now anyone who gets left back and has a birthday from Oct-June will be 19 when they graduate high school. It is what it is.
Both my kids will be 18 when they graduate high school, I was 17, but half of my graduating class was 18(all the kids born after January 1st-we had a 12/31 cutoff back then), with a couple of kids who had been left back being 19, I don't find it unusual at all.