thirty-something
1. adjective Of an unspecified age in one's thirties. He looks like he's in his 50s, but he's really just thirty-something.
2. noun A person who is in their thirties. Usually used in the plural. With so many college students in this town, it's nice to find a place that's geared more for thirty-somethings.
thirty-something (or forty-something, etc.)
an unspecified age between thirty and forty (forty and fifty, etc.). informal