Strictly of legal age, but old men are better lovers for young women, and young men are better lovers for older women.

Why? Many reasons:

1. Their libidos are better matched - older men are starting to slow down just as women's libido increase due to menopause.
2. An older man is more likely to know how to make a woman orgasm, while an older woman is going to be more confident in telling her partner what she wants, which leads to younger women learning how to enjoy sex, and younger men learning how to pleasure a partner.
3. Attraction - men typically find youth attractive, while women typically find seniority to be attractive. This is a natural result of evolution causing men to seek more viable pairing for offspring, and women to seek more experienced men who have demonstrated fortitude and likely have acquired resources to support children.

In society, the knee jerk reaction is to shun or mock pairings of opposite ends of the age spectrum (I decided to post this after seeing Hugh Hefner and Leonardo DiCaprio being the target of mockery) but their relations are the healthiest and best possible match for both parties.

Exceptions to the rules - not all older men have learned how to help their partners orgasm, and not all older women have their libidos rev up to match that of young men - but in general, older<->younger is the ideal pairing sexually.

Edit: Based on the upvote/downvote ratio this is NOT an unpopular opinion. I had no idea so many people agreed with me! 😯