I'm 50, married just once, 20 years now, - although, the last few years the wife and I have come close to calling it quits.
I think divorce at this age is probably more common. I think for most people, this is the age when your job is likely to be most stressful. Usually this is when responsibilities and position on the career ladder peak, but, with the economy recently, wages have not. Kids have either just left or are getting close to leaving. This is an additional stressor, and, often, is a factor in divorce, since lots of people stay together only because of the kids and, once they'r gone, so is the marriage. This is also the age when most women go through menopause. So, even if you are spending time together, it's not always pleasant. With that, too, sex dries up.
Usually, if couples make it to 60, they tend to stay together. Proabably too tired to go out and start a new life.