Any device will degrade from both over use and neglect. Anything, from a tiny electronic watch to an aircraft carrier.
Consumer cameras are designed to be used by consumers, which means often sitting in the closet for months without use.
How many months? don't know, and it depends on too many things to make a firm statement, but easily six months at a time. Back in the film days, consumer film was designed to be able to make images when you shoot some shots of the Christmas tree in December, and some at the beach in July.
Jack, you are asking a huge number of question that seem to be focusing on "best" and how long things will last. You are clearly thinking of an expensive superzoom or a low end DSLR, each of which costs less than $1000.
Just buy it and use it, and enjoy. Leave the worrying to someone else. If you find you don't use it much, sell it. If you find you use it every day and take lots of photos, why would you be sad if it wears out in a few years?
I have a Nikon F that is 40 years old, it still works. I also have a Canon 50D that I like a lot. It has shown zero impact of my use of it. I expect that if I take a lot of photos, in a few years it may show some wear, perhaps the shutter limit will be reached. But if I've taken 100,000 images with it, it won't have owed me anything, I'll be happy. The reality is that by the time I've taken that many images, Moore's law will have made far better cameras so cheap I'll want to buy a Canon 7d mark 3 or whatever is cool.
Relax, buy something and learn to use it.