Old English ripe, of grain, fruit, seed, a field, "ready for reaping, mature," of animals used as food, "fit for eating," from West Germanic *ripijaz (source also of Old Saxon ripi, Middle Dutch ripe, Dutch rijp, Old High German rifi, German reif); related to Old English repan "to reap" (see reap).
Usually explained as "fit for reaping," in which case it would have been originally of grains and extended to all fruit. Figurative use by c. 1200. As "full-grown, developed, finished" (a ripe age) by late 14c. The meaning "ready for some action or effect" (as in the time is ripe) is from late 14c. Of lips, the mouth, "round and full, like ripe fruit," by 1580s. Related: Ripely. The proverb soon ripe, soon rotten is attested by 1540s.