mid-

He's in his mid-thirties — meaning he is roughly around the age of 33-37, as opposed to one's early thirties (aged roughly 30–33) and one's late thirties (aged roughly around 37-39).

a mid-sixteenth-century cathedral.

Back in the mid-’90s, when Cacioppo was at Ohio State University (he is now at the University of Chicago), he and his colleagues sorted undergraduates into three groups—the non-lonely, the sort-of-sometimes lonely, and the lonely.

2013 May 13, Judith Shulevitz, “The Lethality of Loneliness”, in The New Republic, archived from the original on 31 Mar 2015

Since the mid-1980s, when Indonesia first began to clear its bountiful forests on an industrial scale in favour of lucrative palm-oil plantations, “haze” has become an almost annual occurrence in South-East Asia.

2013 June 29, “Unspontaneous combustion”, in The Economist, volume 407, number 8842, page 29