[dmm]

I do research for the US Army. I'll be 39 this summer. Wife and I just had our 5th child a few weeks ago. I'm thinking about returning to grad school.

Warning -- soapbox speech coming:
Age is definitely not just in the mind -- you have to push yourself harder as the years go by -- but most people let themselves get old too soon. They stop growing, and start dying. What a waste. If your goal in life is to retire early and goof off full-time, you'll be dead by 60. Or, if you're not, everyone will wish you were!