30

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

To be younger than a certain age. You can get away with dressing like a teenager when you're still on the right side of 30. I was never sore after working out when I was on the right side of 40!
See also: of, right, side

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

oh dark thirty

A non-specific time in the early morning before the sun has risen. Based on the way in which military time is said aloud. ("Oh" is a common way of saying the number 0.) Why on earth are we meeting at oh dark thirty? The only thing we should be doing at this hour is sleeping! We'll have to leave at oh dark thirty if we want to reach Las Cruces before sundown.
See also: dark, oh, thirty

the sunny side of (an age)

Just a little bit younger than a landmark age, such as 20, 30, 40, etc. The thriller centers on a young journalist on the sunny side of 30 discovering the treacherous world of politics in Washington, D.C. What would you know about a business like this? You're still on the sunny side of 20!
See also: of, side, sunny

zero dark thirty

A non-specific time in the early morning before the sun has risen. Based on the way in which military time is said aloud. Why on earth are we meeting at zero dark thirty? The only thing we should be doing at this hour is sleeping! We'll have to leave at zero dark thirty if we want to reach Las Cruces before sundown.
See also: dark, thirty, zero
Farlex Dictionary of Idioms.

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
Farlex Partner Idioms Dictionary
See also:
  • be (on) the right side of (an age)
  • etc.
  • be (on) the wrong side of (an age)
  • be on the right/wrong side of 40, 50, etc.
  • get on the wrong side of the law
  • over the hill, to be
  • be over the hill
  • sore
  • sore point
  • sore point, a