A young person, not fully developed WordNet 3.0 & Open English WordNet

A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Wikipedia

Individual organism that has not yet reached its adult form, sexual maturity, size;if transition from juvenile to fully mature is a more prolonged process (puberty for example), then juveniles during this transformation are sometimes called subadults Wikidata

An organism that is not sexually mature. OmegaWiki