Your only fifty! That 's not old. You might have another fifteen or twenty years of cycling at a fairly high level.
Road bike? I don't know if a carbon fiber bike with skinny tires is right for you but there are other options: One would be a Randonneur style bike with 650B tires. The 650B tires are almost as fast and much more comfortable than skinny tires. I don't have to tel lyou about our lousy roads. There are also a lot of used steel bikes for sale in the Boston area. Check out CL , yard sales and the metal pile at the dump.