Why are you asking?
I don't think it's age related really - but is dependent on many factors. Phase of your life; whether you want to meet someone. And, of course, financial setup.
If you married too young - then you divorce and try to meet someone else to have kids with.
If you had your kids - and are in mid-life - you may divorce and meet another partner to have your years-after-kids with.
If you are older - it also depends on what you want. DO you want to meet someone else? Or are you OK possibly living the older years on your own. I think in this phase - it also depends a lot on the financial situation, and if you can survive on your own - or whether being roommates is better for both of you.