While its certainly negroid behavior usually, I know a lot of local businesses in my mostly white town banned teenagers because high schoolers were also just little shits and kept shoplifting or getting rowdy. All the ones within walking distance of the school during their lunch time specifically.

But saying "we don't want specific ages" is probably too close to discrimination laws, so they go with the wide net because a kid under like 13 isn't likely to be coming in anyway.