I'm more than ten years younger than you (63) but still consider myself an older traveler.
First - I know this is a Rick Steves forum, and he is the Travel Guru for this group, but I'm just gonna say this (with all due respect) - I don't care what Rick says about "never checking" your luggage! I check my luggage for a very good reason which is that I want to drop it off as soon as I enter the airport and then forget about it until I arrive at my destination.
I don't want to roll it through the airport, get on and off the Plane Train with it, carry it with me to the lounge and keep an eye on it while I'm getting food and drinks, carry it with me to the restroom, babysit it at the gate, carry it on board and wrestle it into an overhead bin - and then do it all in reverse when we land, get it out of the bin, roll it through the airport, take in the restroom, stand in the immigration line with it, etc. NOPE! I'll just grab it off the carousel when I get there, easy peasy. Rick can do what he wants, but I get free checked luggage with Delta and I intend to take advantage of it (I only do nonstop flights.)
Second - We don't rent cars in Europe, but that is a personal preference. I'm happy with a chauffeur taking us door to door without ever having to navigate the route, deal with traffic, stop for gas, or find a parking place (also they can drive into vehicle restricted zones to drop us off.)
For longer distances, we get a taxi or Uber to the train station, and again on the other end to our accommodations. Once we're at our destination we use a taxi or ride share to get around town if it's too far to walk.
Third - We also avoid big cities for the most part. I have no desire to ever go to Paris, Rome, or London again. On our last trip to Italy, we flew in to Naples (big city, but very cool, we loved it) and on our upcoming trip to northern France we're flying into Brussels (big city, but anything's gotta be better than CDG.) And we stay in small towns where it is not only more pleasant and less crowded, but it is less expensive. We get a home base and take day trips from there as the mood strikes.
Also, as I've gotten older, I have less interest in anything that involves crowds, timed entries, or standing in line. At this point in my life I refuse to stand in a line more than ten minutes or so. Nothing - no, not the Mona Lisa, The David, the Crown Jewels, or ANYTHING - is worth standing in line to see. (Anyway, I've seen those/done that and not one of them ranks among my most treasured memories of traveling in Europe.). Basically, I no longer travel to see things but rather to experience things and create memories. And for that, you need to get out of the tourist centers and do a deeper dive. I call it "traveling gently" and that is how we roll now.