Answer To Which Fast

The שערי תשובה (O. Ch 580 ) writes, they  found the Pinkas (Kehilla Records)  and in it was written,“They were Gozer Ta’anis, כ' סיון only for males older than 18 yrs. and females older than 15 yrs.” This is in accordance with the מגן אברהם (576:10) who writes, “When we are גוזר תענית על כל צרה שלא תבא, The minimum ages for fasting,are 15 & 18 years." The ד' צומות we start at ages 12 &13 but all the others we start at the ages of 15 &18