Biomedical Engineering and Modeling & Simulation Engineering. Research in medical simulation, computer-assisted surgery, and geriatric fall injury mitigation. It's common to see profs keep going into their 70s and 80s. A colleague retired around 70 recently, and I found it shocking. I was thinking: "what the hell are you doing? You'll be bored!" On campus, we're kings (to some degree). At home, our wives boss us around.
I'm also a late bloomer, so I appreciate it even more. So I want to savor it and keep going. Moreover, I have two startups that I'm incubating, which will also keep me busy.