I also know a couple with a similar age gap (she is 25 and he is 58, and they met 2 years ago.) 33 years difference. Quite grim. He is biologically old enough to be her grandfather. The young woman is a uni educated professional, and is physically attractive and intelligent, and NOBODY can work out why she's with him. (she met him at the gym.) This man has no assets (not even a residential property as he rents his flat,) and has an average minimum pay job, so it's not money or wealth that she's after. He doesn't even have a car and they get the bus everywhere, or taxis, or they walk...
He never wants to go out socialising, and he doesn't like HER going out, and she just spends the weekends in with him watching TV like a couch potato. She is 25, she should be living her best life, yet she is wasting it with him. Around 6 or 7 of her pals have been abroad twice this year on hen parties, and to Pride Parades, and a couple of weddings, and a big 40th birthday bash, and she has turned them all down 'because Dave doesn't want me to go as he will be 'lonely...' Her pals said 'well bring him along!' She said 'but he doesn't wanna come tho...
'
So he doesn't want to go but doesn't want HER to go anywhere!
SO depressing. 
Her parents have actually gone NC with her as they're so disgusted and upset by it all. They went NC when she moved in with 'Dave' just 5 months after meeting him. Most people 70+ who I know, have better, more exciting social lives than she does. It's so sad to see this vibrant young woman turning into a shadow of her former self since she met this man (2 years ago.)
I know this is purely anecdotal, but I don't know a single 'huge age gap' relationship where it ended well. (I mean 20-25 years +.) I just genuinely believe they're a bad idea. Too much of a power imbalance, and at totally different avenues in life. And the 'yeah but same-age-relationships break up' argument is just silly and weak.