'mid-fifties' definitions:

Definition of 'mid-fifties'

From: WordNet
noun
The time of life between 50 and 60 [syn: fifties, mid- fifties]

Definition of 'mid-fifties'

From: GCIDE
  • mid-fifties \mid-fifties\ n. the time of life between 50 and 60.
  • Syn: fifties. [WordNet 1.5]