prepubescent (adj.)

word-forming element meaning "before," from Old French pre- and Medieval Latin pre-, both from Latin prae (adverb and preposition) "before in time or place," from PIE *peri- (source also of Oscan prai, Umbrian pre, Sanskrit pare "thereupon," Greek parai "at," Gaulish are- "at, before," Lithuanian prie "at," Old Church Slavonic pri "at," Gothic faura, Old English fore "before"), extended form of root *per- (1) "forward," hence "beyond, in front of, before."

The Latin word was active in forming verbs. Also see prae-. Sometimes in Middle English muddled with words in pro- or per-.

1610s, "arriving at puberty," a back-formation from pubescence or else from French pubescent (early 16c.) or directly from Latin pubescentem (nominative pubescens), present participle of pubescere "to reach puberty." By 1760  in biology, "covered with fine short hairs or down."