I'm glad to know I'm not the only one here who isn't a semi-professional racer who can ride centuries backwards without working up a sweat. It sounds like you and I are at about the same developmental point. This past week I went 30.5 miles, 21 miles and 32 miles. My butt, lower back and wrists are limiting factors at this point. It was a few short weeks ago that I topped 20 miles for the first time. I don't have any real performance objectives. At 44 years old with 3 knee surgeries and a shoulder surgery, I am in it for the pleasure and health benefits. I have been entertaining the hopes that I will do a century one day. I eat an energy bar, drink some gatorade, pop a vitamin and swallow a motrin or two before I head out. I drink only the water in my two bottles along the way. With longer distances and warming temps on the horizon, I will have to address the hydration issue.
For me, it's important not to put any unrealistic pressure on myself. I really do simply want to have fun and stay fit. I keep an eye toward improvement without setting any specific goals.