Humans grew to be over 12 feet tall, briefly, within the last 60 thousand years, the thing that knocked them all down to size is that six feet is about the limit before a lapse in judgment and a bad fall onto a rock goes from a bad month to deadly.

That's not going to stop people from breeding people back up so they're 12 feet tall again. You can do it, it's no different than breeding race horses.

Get a natural 7 foot ten foot tall man and an 7 foot ten tall woman, half the kids will be a regression to the mean six foot, but the other half will be 8 feet tall and one of them will be 8 foot 2.
https://www.youtube.com/watch?v=mrFQk6oYgF0