Why would you want a 20 year old wife at age 50. The maturity gap would be almost unbridgeable. The only benefits are sexual and even then the maturity aspect might play a part. Even in my late 20s, the idea of someone who has just left their teens would be deal breaker
If a man at 50 wants to marry, it is usually because he wants kids, otherwise there is no reason to get married at that age. If he wants kids, the woman must be in the fertility age, which is 15 to 35, with the best bet in the 20-30 interval. Just biology. Yes, the maturity gap is big, but if that is the price to pay to have kids ...
As they say, if you have dirty thoughts about 14 year old girl, and want do get rid of them, just spend some time with a 14 year old girl.
Same thing with 50 year old men with 20 year old wives. I am in my early 40s and there is no way I will marry woman in her early 20s, unless she is very special. Sure, 20 year old bodies are attractive, but maturity difference is too great. The movies are fantasies, showing off women at the age of peak physical attractiveness, with just enough immaturity to make the man feel more responsible by contrast, but without any of the quirks of actual immaturity.
Having a 20 year old sex partner is another story. And many women are willing to let you live your fantasy, for a time, for a price...