My first century was decided on the fly too. I was initally going to do a long loop around Lake candlewood, going out to NY rt 22 rather than riding closely through Sherman and New Fairfield. When I got to the point of decision, I decided to ride to Kent. After riding to Kent, I decided "That wasn't too bad, I wonder how far it is to the MA border?"

Answer: 51 miles-- and 51 miles back.