Well, what is age appropriate. I think a man marrying a gal 5 to 15 years younger is a good thing, especially if he provides for her. I think a woman marrying someone much younger, is going to have issues at some point in time.
It all comes down to the same things, regardless of the country or the ethnicity. You grow together thru respectful argument, and requires you to listen and adapt to your partner. If you don’t do that, then it doesn’t go anywhere.
For a 40 year old man, the main reason to marry is to have kids, which means that it makes sense to seek a woman who is still in her most fertile years (20 to 35). If he's not interested in kids, it makes more sense to just live with her, and avoid the risks of divorce-rape.