cradle-snatcher 
noun derogatory
A person who marries or has a sexual relationship with a much younger person.Man oh man, Jay, I never knew you were such a cradle-snatcher!...
- My friends ‘back home’ do not understand this association and I'm afraid have branded me as a cradle-snatcher, but that is their problem.
- Amusingly he heard the words ‘cradle-snatcher’ and ‘gold-digger’ come up more than once.