I have been work camping this winter in a large park and can say I have met people that scare me to death. Big 5er, ran over the turn guards, when I tried to explain where the hookups were he was so hard of hearing even speaking directly at him he did not acknowledge anything I said. He was very unsteady on his feet.
All that said the people who care about you and are around you all the time can be of a big help. They will notice things you don't, and if your open and listen they can help you make a decision. Other things are daylight driving only shorter trips or more overnights on the way. Instead of 400 miles a day do 200. Walmart loves ya. Smaller rig that's easier to drive, also an option.
Lastly aarp has senior driving courses that can really help your confidence and also help decide when it's time.
Age is not important, I do a high performance driving school everytime I'm home. There is one instructor in his 80s who will spank you on the track.
Good luck be safe