adj. young; characterized by youth-like strength and spirit
adv. youthfully, in a spirited manner
n. youth; youth-like strength and spirit
v. to make or become young; to regain the strength of youth

Goraan! I feel younger than I have in many an age.
(Paarthurnax, 0009E073)

For dragons, may be closer in meaning to liveliness, spirit, and strength that would be characteristic of youth, rather than youth itself.