1) It's not called POTS Syndrome. The S in POTS stands for Syndrome, so saying "POTS Syndrome" is redundant.
2) I haven't read/heard that it affects girls ages 12-20 the most. It definitely affects females more than males, but the typical age range is 12-50 years old (source).
3) I'm not sure if it's entirely accurate to say that most kids "grow out of POTS". Some do, but others have different severity of symptoms throughout their lives. I couldn't find any articles that suggest most kids grow out of it.