Dictionary Definition:
Vaya1 (& vayo) (nt.) [Vedic vayas vitality, age; to be distinguished from another vayas meaning "fowl." The latter is probably meant at Dhtp 232 (& Dhtm 332) with defn "gamane." The etym. of vayo (age) is connected with Sk. vīra=Lat. vir. man, hero, vīs strength; Gr. i)/s sinew, i)/fios strong; Sk. vīḍayati to make fast, also veśati; whereas vayas (fowl) corresponds with Sk. vayasa (bird) & viḥ to Gr. ai)eto/s eagle, oi)wno/s bird of prey, Lat. avis bird] age, especially young age, prime, youth; meaning "old age" when characterized as such or contrasted to youth (the ord. term for old age being jarā). Three "ages" or "periods of life" are usually distinguished, viz. paṭhama˚ youth, majjhima˚ middle age, pacchima˚ old age, e. g. at J i.79; Vism 619; DhAiii.133. -- vayo anuppatta one who has attained old age, old D i.48 (=pacchima -- vayaŋ anuppatta DA i.143); Sn pp. 50, 92. -- Cp. Dh 260; J i.138 (vayo -- harā kesā); Vism 619 (the 3 vayas with subdivisions into dasakas or decades of life); Mhvs 2, 26 (ekūnatiŋso vayasā 29 years of age); PvA 5 (paṭhama -- vaye when quite young), 36 (id.; just grown up). In cpds. vaya˚.
-- kalyāṇa charm of youth DhA i.387. -- ppatta come of age, fit to marry (at 16) VvA 120; PvA 3, 112; ThA 266.