From Longman Dictionary of Contemporary Englishprepubescentpre‧pu‧bes‧cent /ˌpriːpjuːˈbesənt◂/ adjective formal HBHrelating to the time just before a child reaches puberty
Examples from the Corpus
prepubescent• Brassieres upholstered with foam rubber were produced as beauty aids even for the well-endowed and even for prepubescent girls. 