Should Dad Be Traveling at His Age?

QUESTION: "My father is 84 and still traveling the world. Though he goes with tour groups, each time he comes home he mentions the difficulty he had keeping up with the group, navigating the terrain, or tolerating the food. I have noticed that dad has more difficulty walking than in the past; he seems less steady on his feet and moves slower than he used to, though some of that is expected with age. I worry that I will receive a call from a distant location that dad has had an accident or has passed, and I won’t be there for him. I do not want to discourage him from doing what he wants, yet I wonder if I should. When is it time to stop traveling?" - READER