Don't jump in with crazy miles without building up to the miles unless you want to risk injury and suffer needlessly. I'm old, and if you want to be an "old cyclist" use common sense and build endurance as well as intensity over time. Three weeks of building and fourth week recovery is a good model. Then proceed to build again. Saturday I did over 5 hours through rollers and in Texas heat. First Saturday in October I will do a century with about 4500' of elevation but no really hard climbs. The "kids" in their 30s and 40s are amazed when I pass some of them on the hills on a fixed gear. There's no short cut to fitness and speed and attempts to short cut the process usually ends in injury or burnout. Have fun.
