Hi m~nien,
My dad is 68 and we work out regularly together. He does 25 minutes on the treadmill, 15 minutes on a lifecycle and about 45 minutes of weight training (nautilus machines). Now of course he wasn't able to do this when he first started but he's getting stronger all the time and is like a teenager in his enthusiasm. It sounds to me like you are also doing really well. I'm 40 and twenty minutes on an elliptical nearly does me in!
I started a running program a few weeks ago and for the first week or two I thought my body was going to give out. My legs, hips, shins and ankles were killing me between runs but eventually all of the pain went away. Today I ran 2.25 miles in the morning and 1.25 miles in the evening and I can honestly say that I'm totally pain free as I type this. The body simply adjusts over time and things become easier.
My adivce would simply be to keep moving each day as the body allows. I promise that it will get easier and the soreness will cease to be a problem. God knew what he was doing when he created us and as the article says.....the body is begging to MOVE.
Happy exercising!
Dave