The very lightest touch a person can detect is called the sensory threshold. After age 25, men, and presumably women, have a slight decline in sensory threshold. Between ages 65 and 75, the sensory decline is greater. But have no fear, there’s plenty of feeling left at any age to have a great time.
I know of one 85-year-old man who has admitted jerking off all the time and enjoying it as much as he has at any age.