Here is my personal take on the situation. I too am 60+, 64 actually. I don't like to have more than one large project going at a time, however I don't count smaller things that I can finish in a few days.
A simple baby quilt, a small wall hanging, using up some scraps to make strip blocks; those are the kinds of things I allow myself to start anytime I feel like I need a break from the large project I am working on. Nothing with a tricky or complex pattern, maybe a panel to add a few blocks and borders around, or some simple 9Ps. Well, you get the idea.
This way, I stay true to having only one major project at a time, while still allowing myself some sides for variety. Sort of like having the main course of a meal, the roast, but adding potatoes and salad for balance and interest. No one wants to just eat roast all the time. :D