a. 1. Not yet mature or aged; young. “Two youthful knights.” Dryden. Also used figuratively. “The youthful season of the year.” Shak. [ 1913 Webster ]

2. Of or pertaining to the early part of life; suitable to early life; as, youthful days; youthful sports. “Warm, youthful blood.” Shak. “Youthful thoughts.” Milton. [ 1913 Webster ]

3. Fresh; vigorous, as in youth. [ 1913 Webster ]

After millions of millions of ages . . . still youthful and flourishing. Bentley. [ 1913 Webster ]

Syn. -- Puerile; juvenile. -- Youthful, Puerile, Juvenile. Puerile is always used in a bad sense, or at least in the sense of what is suitable to a boy only; as, puerile objections, puerile amusements, etc. Juvenile is sometimes taken in a bad sense, as when speaking of youth in contrast with manhood; as, juvenile tricks; a juvenile performance. Youthful is commonly employed in a good sense; as, youthful aspirations; or at least by way of extenuating; as, youthful indiscretions. “Some men, imagining themselves possessed with a divine fury, often fall into toys and trifles, which are only puerilities.” Dryden. “Raw, juvenile writers imagine that, by pouring forth figures often, they render their compositions warm and animated.” Blair. [ 1913 Webster ]

-- Youth"ful*ly, adv. -- Youth"ful*ness, n. [ 1913 Webster ]