Well I'm still doing part time hours @ almost 71, with me it's not about the money it's because I enjoy my work and the thought of retirement scares the sh*t out of me.
I have to have a reason to get up in the mornings, it's nice knowing you have cash in your back pocket and not worrying too much about paying the bills.
My wife who is now 65 also comes with me about 3 days a week and does a little bit.