What is his goal with the dating? Does he want kids? Does he want to get married again?
If he wants kids, I'd say mid 30's with a woman that doesn't have kids but wants one. If he doesn't want kids, I'd say mid 30's- early 40's. The more you increase the age range, the harder it is to find a good woman. Good women get scooped up. Some good divorcees come on the market but most of them have issues and you have to be extra critical of what they are showing you.
That said, I'm in my mid 40's and if I was to be single again, I'd go out of the country. Whether looking for a wife, or just having fun, women are way better outside the US now.