I think if you asked anyone in Thailand, they would say it is acceptable to be in a total mismatched relationship (age, looks, wealth, etc.)
That is the big trade-off.
A young woman of limited education and financial means may settle for an older man, (old enough to be her grandfather) if her needs were being met.
Of course she would 100% rather be with someone her own age, handsome and has financial means.
But the reality in Thailand is this is not the case.
Most middle class and above Thai men, do not care for uneducated, dark, Isaan woman.
They prefer the white as ghost, bleached city girls.
The poorer woman of Isaan and other rural areas often have to settle for a local Thai man, that may be extremely financially limited and other worse problems.
Can a young woman be happy with someone 40 years her age?
That is a question only they can answer.
Sometimes having something like a home, land, car, spending money, etc. is better than being dirt poor?
This decision is up to each and every woman.
If you can understand the sheer level of poverty in some areas of Thailand, this would make more sense to you.
As long as they are both happy, it between them.