When I was growing up the Browning's, my next door neighbors, had a pet squirrel. Max had a huge cage out back with his own little house and they fed him daily. He ate produce and nuts and generally led a life of comfort.
Every so often Wimpy, the grandpa, would cut fresh branches and put them in his cage. The cage was right where we played every day so we spent plenty of time coaxing him and paying attention to him. Rusty and Sissy were the kids who actually lived there but we 3 kids were there almost as much they were. In fact we didn't know the difference between their backyard and ours and it was the same for them.
I don't know how long Max was there before we moved in. (I was 10) but I know he was still alive into my 30's. I don't know how long wild squirrels live but Max had a good long life.