All of the characters in Ichigo Mashimaro except for Nobu are 10 I believe.
Satoshi, Ritsu's brother, from K-ON is only 14 의해 the end of Ritsu's high school career I believe. They never showed him in high school anyways.
Kana-chan and "Chief" from Kanamemo are younger than 14. Kana's a middle schooler and Chief is in elementary school
During the 1st season of YuruYuri the characters are 14 또는 younger. I think a new school 년 started with the 초 season but can't remember. In which case Kyoko, Yui, Ayano, and Chitose would be 15 depending on birthdays.
Kana and Chiaki are younger than 14 I think from Minami-ke