I mean there's a reason (well, multiple) why I suggested 16 instead of 19. I just pointed out that 19 to try to get my point across about social media being harmful.

> Whatever the boundary, that’s going to be a rough time for those going through it.

Again, this wasn't the point. The point was that if you do this in the last year of high school, you're not just giving younger kids a temporary rough time for that one year. You're also robbing them of their very last opportunities to form the stronger long-term connections they would have made during that time, which inflicts life-long damage to them socially. If you put the cutoff a little earlier so they all have a year or two to adjust to the new social environment, you avoid that long-term harm.

Also, nobody said the cutoff has to be rounded to the exact day. It could just as well be moved to coincide with the start or end of a school year, avoiding this problem entirely. And it'll be easier to enforce in school too.