Many young girls choose to wear training bras at the beginning of puberty, generally around the ages of 8-13. There are a variety of reasons for this, including the following:
1. Even if the girl does not have breasts yet, if her friends are wearing training bras she may feel that it is necessary. This is especially true for girls who change in locker rooms etc.
2. Girls who are beginning puberty may want to wear a training bra so that the changes in their breasts are not as noticeable or are covered up.