From Latin 'adolescere' (to grow up), sharing root 'alere' (to nourish) with 'adult' — its completed form.
The period of development between childhood and adulthood.
From Latin adolescentia (youth), the abstract noun from adolescens (growing up), the present participle of adolescere (to grow up, mature), a compound of ad- (toward) + alescere (to grow, be nourished), the inchoative form of alere (to nourish, feed). Latin alere derives from PIE *h2el- (to grow, nourish), which also produced Old English alan (to nourish), Latin altus (high, deep — literally "grown"), and Latin alimentum (nourishment). The semantic core is organic growth toward maturity
Latin 'adolescere' (to grow up) and 'adultus' (grown up) share the same root 'alere' (to nourish). An adolescent is still growing; an adult has finished growing. The same root gives us 'alma mater' (nourishing mother) — the school that nourished your growth.