Important to stay active and flexible with age. Even if it means giving up that diamond frame. Mixtes have a lower top tube, are easier to mount and dismount, which means you can go larger size for a more stable and compliant ride. And they make great commuter, cruiser, tourer bikes. The Windsor Kensington has a nice ride quality and is a great value at < $600 but may not be suitable for heavy duty touring. Rivendell Bicycle Works is a good option if price is not of concern.