rob the cradle
a cradle robber someone who has a romantic or sexual relationship with a much younger partner

[TahlilGaran] Dictionary of Contemporary English ▲

rob the cradle
[American, humorous]
a cradle-robber - someone who has a romantic or sexual relationship with a much younger partner.
People are always telling her she's robbing the cradle. She's ten years older than Joe.

[TahlilGaran] English Idioms Dictionary ▲

rob the cradle
to marry a person much younger than oneself
People said that my boss was robbing the cradle when he married the young woman at our company.

[TahlilGaran] English Idioms Dictionary ▲

rob the cradle
v. phr., informal To have dates with or marry a person much younger than yourself.
When the old woman married a young man, everyone said she was robbing the cradle. -

[TahlilGaran] English Idioms Dictionary ▲