From Longman Dictionary of Contemporary Englishin your middle twenties/thirties etcin your middle twenties/thirties etcTMCAGEabout 25,35 etc years old → middle
Examples from the Corpus
in your middle twenties/thirties etc• Among these was a tall firebrand of a patriot in his middle twenties.• You must be in your middle thirties.• Owen and the Victoria Centre Owen is in his middle thirties and his working background is in education.• While still in his middle twenties, he was offered a teaching position at an Ivy League university. 