Mileage isn't you problem with those numbers. I think that some intervals and what I call hill attacks would be the best bet, I am no one to act like an expert. Allegheny Jet's reply has some good thoughts, try his advice and maybe look into using the 50+ Racing Forum for training tips that will allow you to increase your pace and speed. Not as a racing program but they helped me when I asked about just establishing a base to return to cycling. Hope you get things up to your standards, you are to be admired after two cancer battles. Respect!

Bill