Exactly. Older folks whose kids are self-sufficient are able to focus their time and energy into their work - even more so than twenty-somethings who are still wrapped-up in life's dramas associated with being young. And they have a lot of experience to boot.

and, let's face it, many of them like having the excuse of long hours to stay away from a family they have grown tired of. My brother told me once he had kids he finally understood the joy of mowing the lawn; you get time away from the kids and wife and its so loud they never think to come bother you and it's work so they don't have the excuse that you are just goofing off

That reminds me of a joke:

Three men are talking: A programmer, a doctor, and a lawyer. The lawyer says, "Man, the only way is to have a mistress. With all these divorce suits, it's terrible. The only way is to have a mistress." The doctor says, "Are you kidding? With all the STDs out there, you want a wife and that's it." The programmer says, "You need both a wife and a mistress. Because when you're not with the mistress, she'll assume you're with your wife, and when you're not with your wife, she'll assume you're with your mistress, and THAT leaves you more time to be in the lab programming!"

(Found on http://stackoverflow.com/questions/234075)