The Collaborative International Dictionary
Youthful \Youth"ful\, a.
Not yet mature or aged; young. ``Two youthful knights.''
--Dryden. Also used figuratively. ``The youthful season of the year.''
--Shak.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.-
Fresh; vigorous, as in youth.
After millions of millions of ages . . . still youthful and flourishing.
--Bentley.Syn: Puerile; juvenile.
Usage: 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.
Wiktionary
adv. In a youthful manner.
WordNet
adv. in a youthful manner; "he is still youthfully enthusiastic"
Usage examples of "youthfully".
Expecting Brule, it was disconcerting to see instead a tall, lean figure whose youthfully graceful shoulders and blond hair she instantly recognized.
Edgar never saw her engaged by Sir Sedley, but he thought her youthfully grateful, and esteemed her the more, or beheld her as a mere coquette, and ceased to esteem her at all.
He had known her some eight years since, shortly before the Avellanos had left Europe for good, as a tall girl of sixteen, youthfully austere, and of a character already so formed that she ventured to treat slightingly his pose of disabused wisdom.
For instance, he might be described as slender, skinny, thin, reedlike, Ichabod Crane-ish, lean, lanky, bony, scrawny, narrow or youthfully fit.
She was both youthfully old and oldly youthful, a peculiar blend of overage flapper and vivacious dowager.