I completed a 10.4 mi loop with some slow narrow bridges and hairpin turns with a 17.0 MPH average yesterday. I turn 60 tomorrow. I have been riding since I was 5 yr old, but I have never been faster than I am today.
I had a Sirrus Hybrid. I could only manage a 15 mph average on this same loop. I just bought a carbon fiber road bike. It is just as comfortable, but I enjoy it more because I got tired of the upright riding position adding so much wind resistance. If you get a properly sized road bike it will be comfortable. The carbon fiber surely does reduce the vibration.