inmaduro
/immaˈduɾo/ · B2 · adj
unripe
🍏 in- (not) + maduro (ripe) = not ripe, unripe, immature
Spanish maduro means ripe or mature, and the prefix in- (often im- before m) negates it. So inmaduro is the opposite of ripe fruit, and by extension a person who has not matured yet.