Toy boy is an informal, chiefly British term for a young man who is having a sexual relationship with a much older woman. 'Much older' sounds rather vague but if it can be replaced by the shocked / disgusted / admiring / envious (delete as appropriate) 'She could be his mother!', you're on the right track.

Notably, except for an occasional nonce formation, there is no such thing as a toy girl. Are girls less fun? I guess, from the point of view of biology and evolution, they are.

When a man is having a sexual relationship with a much younger woman, he may seem to have lots of fun, but don't be fooled. By choosing a younger partner, he has a better chance of producing healthy offspring and therefore transmitting his precious genes to the next generation and ultimately ensuring the survival of the human race. Pretty serious stuff, if you ask me.

On the other hand, when a woman is having a sexual relationship with a much younger man, producing offspring is not really the point. Older women do it just for fun. Hence toy boys.

Definitely something to look forward to in my old age. Apart from the free bus pass, of course.