Be (on) the wrong side of (an age) informal
Look older than a certain age
Though she is trying to dress young, she's still on the wrong side of 40.
My friend and I are the same age, but she's on the wrong side of 50.
To be in a poor condition.
To be extremely old (a joke or a story)
Used to indicate that the age at which a person's consent to sexual relations is legitimate.
Be nearly a particular age
The verb "be" should be conjugated according to its tense.
1. Doing something extremely well
2. Behaving in an extreme or remarkable manner
1. Holly was in rare form during her speech, so she got the first prize in the competition last night.
2. Corrine: I'm going to buy Christmas presents for everybody. Do you want to go with me?
Laura: Oh...My kids are in rare form today, so I cannot go with you. Sorry!