Ask Lance - he would tell you that peak performance drops fast after the mid-30's .

I am 52 and I found that no matter how many miles I log, I have to really watch my diet closely to stay at my ideal weight. I think the"25 lbs over ideal weight" is somewhat of an anchor for your speed.

That being said, to be riding 4500 miles per year at age 61 is excellent. I am a Physician and I frequently send patients to Nursing Homes in their 60's because they have never exercised or cared for their bodies. You should be proud of yourself.