WordNet (r) 3.0 (2006):

young man
    n 1: a teenager or a young adult male [syn: young buck, young
         man]
    2: a man who is the lover of a girl or young woman; "if I'd
       known he was her boyfriend I wouldn't have asked" [syn:
       boyfriend, fellow, beau, swain, young man]

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "young man":
   Casanova, Don Juan, Lothario, Romeo, amoroso, beau, boy, boyfriend,
   bub, bubba, buck, bud, buddy, caballero, cavalier,
   cavaliere servente, colt, cub, esquire, fellow, flame, fledgling,
   gallant, gentleman friend, gigolo, hobbledehoy, inamorato, lad,
   laddie, lady-killer, love-maker, man, manchild, master, muchacho,
   necker, old man, petter, philanderer, pup, puppy, schoolboy,
   seducer, sheik, sonny, sonny boy, squire, sugar daddy, swain,
   whelp, youth