I finally took my bike to a shop for a cleaning and tune-up. I haven't ridden in a while, mainly because of my knees, but I miss it. My doctor recommended taking some ibuprofen an hour before riding as he believes it's simply age-related arthritis. I hope he's right. Even if he isn't, I estimate the ride from my house to work will take about 20 minutes (cf. 45 by bus or train), which isn't even long enough to work up a sweat.
I'm not planning to ride the North Shore Century this year, though. Let's take it slow. If I'm up to 50 km without pain by mid-July, I'll reconsider.