Well, this thread has been a good one, so I'll bite
I had a "hobby" which kept me in pretty trim condition up until my mid-twenties, but between getting out of that particular activity and the demands of work and night study, I lost fitness.
Coming back in a big way this year, though. I've been working back up (carefully) during the summer, and now it's thirty each of squats, sit-ups and press-ups to start the day, plus plenty of walking and some jogging. A visit to a physio sometime soon to see about the knees, and then it'll be onto one of the many good gyms in the city. I see some appealing 'boot camp' classes around town