The Collaborative International Dictionary of English v.0.48:
mid-thirties \mid-thirties\ n. the time of life between 30 and 40. Syn: thirties, thirty-something. [WordNet 1.5]WordNet (r) 3.0 (2006):
mid-thirties n 1: the time of life between 30 and 40 [syn: thirties, mid- thirties, thirty-something]