Leave him alone to do whatever, it is his life and none of your business.He is probably very lonely, after the death of his wife and these sites may bring him solace.
Much later on if you think he is still viewing , you could tactfully explain just how costly some sites are, just by way of casual conversation.
Even tho he is 86 in body, in spirit at times he may feel about 20, nothing distateful or disturbing about that in my view.