You’re too young to buy a thong if:
- you’re too young to have your driver’s permit.
- you’re not big enough to ride the big kid rides at amusement parks.
- you still wear a training bra.
- you don’t pay the adult fare at the movies.
- your mom still packs your lunch.
Feel free to add your own. Not that I’m THAT old, but back when i was in high school (not to even mention middle school!) the only girls that wore thongs were hussies.
I’m only surley because when I was shopping at Victoria’s Secret this evening I was blocked out of the underwear tables by a throng of 10 girls that couldn’t have been over 12. The little sluts. 
Of course, being older and actually just physically bigger than them, you could have just pushed them out of the way like I did