I know you can't help who you fall for, but I have honestly never 'got' why a young woman just out of her teens would want to be in a relationship with a 40 year old man. Virtually old enough to be her dad. It is a massive power imbalance as some people have said, and it is a bit icky. I can see why HE wants to be with a young fit young woman, but I can't see why SHE wants to be with him. Not long term anyway!
I am guessing that he comes across and as older, wiser, mature, and sensible, not a flighty, flaky buggar - or snappy and a bit aggressive like (some) younger 'men. And she's all excited - with these 'he'll look after me and nurture me and guide me and teach me so much, and 'older men are so good in bed' kind of thoughts.
But I don't think many of these relationships can work long-term. I know some people come onto these threads, and say their parents/aunt & uncle/nan and grandad etc etc etc, had a 25 year age gap and they are still together 40 years later etc etc etc, but IMO, these are the exception, rather than the rule.
And quite honestly I have known very VERY few age-gap couples in real life. There was one couple who I met who were neighbours of DH when I first met him... He was 42, she was 21. They had started seeing each other at 36 and 15. Yes really. It was 30 years ago, and even then people were like
He was a friend of the girl's dad, and it caused an absolute shitstorm.
They got married at 19 and 40, and most of the 2 sides of the families, didn't come. There was around 20 people out of 50 invited who actually came. They had 2 kids close together when she was 21 and 23, and when the kids were 15 and 13 (and she was 36 and he was 57,) she left him. Moved in with her parents for a while til she was allocated a council house. Said she hated being with a boring old man who moaned all day, and had constant health ailments. And she had no intention of being his 'carer.'
Another couple are one I know now. She is 29 and he is 57. For some reason, she is obsessed with him, and is his admin clerk, his nurse, his maid, his secretary, his sex partner, and everything he wants her to be. They have been together for 3 years, and her friends say she has turned from a vibrant, go-getting, fun-loving, ambitious mid 20-something, to a boring, dull, miserable, old woman who NEVER goes out with people her own age now, and dresses like she's 65. Their words. Don't shoot the messenger!
I also used to know a woman, some 15 years ago who was 42-43, and was with a bloke 20 years younger. All she did was brag about how 'great' the sex was, how she would HATE to be with an old man in his 30s or 40s like us other women in the office, and how much better in bed her man was (
) and how he had soooo much energy. Upshot was, he was dull and boring, never acknowledged her friends, rarely spoke to her family, and sat on his arse all day, refusing to get a job, just living off her. Utter cocklodger. Yet she thought we were all jealous of her with our 'ancient' husbands between 33 and 46. PMSL!
But yeah tl;dr. I am not a fan of age gap relationships, I would never get into one, and I can't see how they can work out long term.