be on the right/wrong side of 40, 50, etc.

be (on) the wrong side of (an age)

To be older than a certain age. Why is she dressing like a teenager when she is clearly the wrong side of 40? I'm sore after every workout these days, so I'm definitely on the wrong side of 30!See also: of, side, wrong

be on the ˌright/ˌwrong side of ˈ40, ˈ50, etc.

(informal, often humorous) be younger/older than 40, 50, etc: ‘How old is she?’ ‘On the wrong side of forty, I’d say.’See also: of, on, right, side, wrong