mutton dressed (up) as lamb

A disparaging term for an older woman who tries unsuccessfully to look much younger or finds herself attractive in the style of younger women. Primarily heard in UK. I don't know what she's thinking wearing a dress like that. She looks like mutton dressed as lamb!

mutton dressed as lamb

mutton dressed up as lamb

BRITISH

If you describe a middle-aged or old woman as mutton dressed as lamb or mutton dressed up as lamb, you mean she dresses in a style which is suitable only for a younger woman. I'm always careful to avoid looking like mutton dressed as lamb. Note: Mutton is the meat of an adult sheep, and lamb is the meat of a young sheep, as well as being the name of the animal itself.

mutton dressed as lamb

a middle-aged or old woman dressed in a style suitable for a much younger woman. British informal

Mutton occurs in various derogatory contexts relating to women. It has been used as a slang term for prostitutes from the early 16th century, for example, while the phrase hawk your mutton means ‘flaunt your sexual attractiveness’ or (of a prostitute) ‘solicit for clients’.

1988 Salman Rushdie The Satanic Verses Mutton dressed as lamb, fifty plus and batting her eyelashes like an eighteen-year-old.