Why are most 6-12th grade female students SO IMMATURE

Because they are young and trying to grow up. Some grow out of it, some don't. Some never enter that phase at all. That's the difficult part about dating, あなた have to find the person whose personality fits yours and it takes time and effort. Do not fret, there are females who are not like this, they just may not be out and about and as easy to find. If あなた are genuinely serious about finding a girl not like this, then look in places あなた don't normally look. Talk to もっと見る people and widen あなた social circle.

I actually know many young girls even younger than 12 who are far もっと見る mature than most people. I think the smarter a girl is and the もっと見る confident she is about herself goes a long way. I'd rather have a mature 10-15 year-old girl be my babysitter than the immature seniors and 20years old.