Carol - My heart goes out to you. I'm 85 also and in my heart I knew I was coming up on a time when I wouldn't be able to drive the RV. I couldn't face that it was that time! Maybe just one more trip? Maybe just go close to home? Maybe get a smaller van? I was in denial for awhile. Those years between 70's and 80's go by so fast! Only YOU can know if you are able to do this. If you are eager to go, you can practice, practice, practice. No one is born knowing how to drive an RV. However, if you are dreading HAVING to go, perhaps you need to dig in your heels and decide you don't want the stress.
When my husband died, we had a huge motorhome with 3 slides sitting in the yard. I was way too intimidated to even try driving it. Instead, I took the loss and bought a Class C and my son helped me learn to drive it. Yes, in an empty parking lot - over and over making turns without running over curbs. He also had me backing in between the white parking lines - over and over. But I was 20 years younger then. I'm not saying what was right for me is right for you and Bill. Last year, I just knew when I found myself in tears every time I went out with the RV that the stress was too much and I got rid of my Pleasure Way. Sure I miss going, but quite honestly if I really wanted to travel there are a lot of options and, by the way, even paying hotels and meals isn't all that more expensive than owning an RV.
Guess what I'm saying is face your strengths and weaknesses, your comfort zone, your eagerness to try (or lack of) and perhaps plan a getaway for the two of you that doesn't include the RV. Do more car driving in and out of traffic areas, on freeways, etc. As for Mexico, that's another whole issue. Think you probably need to deal with the "whether to drive or not" issue first!
Having said all that: The last time I was in Q I overheard a man talking about his drive to get there. He was 92 and was driving a huge diesel pusher. Yup, it can be done. Of course, I wanted to make sure I didn't leave and get on the road when he did!!
Good luck with whatever you decide and know that there are many, many gals here who are rooting for you no matter what!