A person with such a sexual preference is a gerontophile. The word gerontophilia was coined in 1901 by psychiatrist Richard von Krafft-Ebing. It derives from Greek: geron, meaning “old person” and philie, meaning “love”.

What do you call the much younger girlfriend of an older man?

A manther is the male version of a cougar, or a middle-aged woman who has the hots for younger men. Manthers are older men who pursue partners significantly younger than them.