Hey, I have a Specialized Tarmac Expert. Yes, my bike is a man's bike.. XS.

I can tell you that it is an aggressive frame/fit. He is not going to like it if he has lower back problems I don't think. It's fast and peppy but not made for comfort at all. It's a racing frame. I'm pretty stretched out on mine and have lower back pain from the position from time to time.

The Robaix is less aggressive and built more for comfort.

I know you weren't asking about this, but just figured I would throw my experience with the Tarmac out there.