The Collaborative International Dictionary of English v.0.48:

Salad days \Sal"ad days`\, n. pl.
   a period when a person is young and inexperienced.
   [1913 Webster]

WordNet (r) 3.0 (2006):

salad days
    n 1: the best time of youth [syn: bloom, bloom of youth,
         salad days]

Moby Thesaurus II by Grady Ward, 1.0:

22 Moby Thesaurus words for "salad days":
   bloom, budtime, early years, florescence, flowering time, jeunesse,
   juvenescence, juvenility, my burning youth, my green age,
   prime of life, seedtime of life, springtime of life, tender age,
   tenderness, young blood, youngness, youth, youthfulness, youthhead,
   youthhood, youthiness