There was a bad experience in my family. A grandfather lost his wife when they were both in their early 70s. After a few years of living on his own, he decided it was a lot of work, and he also missed the companionship. There had been a number of neighbor widows after him for some time, and he finally picked one.
She was about 15 years younger, and she promised to take care of him as he aged. But she demanded that he change his will to write out his three children (who he loved) and make her his sole heir, with her children (from her prior marriage) as secondary. She badgered him about it long enough that he finally gave in and did it (none of his three children lived nearby).
Unbeknown to him, she was already in failing health, and he soon found himself taking care of her instead of the other way around. Eventually he had to hire people to take care of them both. When he died, she got everything (refused to even let any of his children have even so much as a photograph). When she died, her children got everything.
Sad story, but these things happen.