If he's married to a 60 year-old woman, he's married to someone who, on average, is physiologically ten years younger and thus likely healthier and more vigorous, physically and mentally.
When she’s older: Does age gap matter in a relationship?
If an 80-year-old man is married to a 75-year-old, physiologically 70, even if she still loves him, she may feel he's an albatross and he may feel he's a burden.