This book has probably been recommended here before. Maybe by me. https://www.amazon.com/Friel-Cycling...SIN=B004WIQJDS
I've been reading it since I was 45. I did back off a bit at 52 when I was worried about an increasing risk of ayortic aneurism due to an abnormal heart. My heart surgeon fixed me up over three surgeries so that I could get back to exercising in the style to which I've been accustomed.