This topic is close to me right now, having come back to riding three months ago after 12 years of a sedentary life.

For the returning cyclist, especially one who used to race, I'd suggest taking it very slowly but ride often. Increase your mileage and your effort as long as it doesn't hurt, but if you have pain, back off because your muscles are likely to be stronger and get stronger faster than the ligaments and connective tissues. I'd also recommend re-adjusting your goals because trying to compete with your former self will only make you unhappy. Embrace all the other aspects of riding - social, familial, touring, and simply being out and enjoying the outdoors. It's a good life and a great activity.

-soma5