The Collaborative International Dictionary of English v.0.48:

Teens \Teens\, n. pl. [See Ten.]
   The years of one's age having the termination -teen,
   beginning with thirteen and ending with nineteen; as, a girl
   in her teens.
   [1913 Webster]

WordNet (r) 3.0 (2006):

teens
    n 1: the time of life between the ages of 12 and 20
    2: all the numbers that end in -teen

Moby Thesaurus II by Grady Ward, 1.0:

53 Moby Thesaurus words for "teens":
   L, Sexagesima, awkward age, boxcar, boxcars, dozen, duodecimo,
   eighty, eleven, fifteen, fifty, five and twenty, fortnight, forty,
   four and twenty, fourscore, fourscore and ten, fourteen,
   half a hundred, long dozen, ninety, nonagenarian, octogenarian,
   quindecennial, quindecim, quindecima, quindene, score,
   septuagenarian, seventy, sexagenarian, sexagenary,
   sexagesimo-quarto, sixteen, sixteenmo, sixty, sixty-four,
   sixty-fourmo, teen age, thirteen, thirty-two, thirty-twomo,
   threescore, threescore and ten, twelve, twelvemo, twenty,
   twenty-five, twenty-four, twenty-fourmo, two dozen, two weeks,
   twoscore