I'm not surprised that there physical benefits from exercising with increasing age. I'm only 51 but I can clearly feel them. I also think that there other advantages and disadvantages about exercising "later" in life.
Throughout my youth, until grad school, I was very active. I hurt my back in grad school and allowed it to drastically diminish my activity due to fear of re-injuring it. Stupidest thing I have ever done.
I started getting back into shape after shape after the birth of my kids, plateaued when I was in ok shape and then a few years ago, when I was about 45 years old, started going to Curves/Ladies Workout Express to add easy strength training. That rapidly escalated; I ramped up my in line skating (sometimes 50 miles per week), added hiking and biking, added karate. Now that I am 51 I am exercising, hard, about 8-10 hours a week. It was much easier once I figured that I can skate, hike and bike year around.
What I have noticed is that I am the strongest I have been since high school. Due to karate I can feel muscles that were never really developed before. My stamina is better as well as long as I am not walking up a hill when my excess weight really becomes noticeable. I can hike at a fast pace or skate for several hours. Well, due to poor technique I'm like the Janis Joplin song, "I don't go too fast but I go pretty far" but it is still an excellent workout. In karate I have more stamina than most of the other black belt women that are 15 years younger than I am.
Endorphins are my friend. I almost always get a runner's high when I exercise hard. If something is hurting then I get an even more intense euphoric feeling and the pain usually magically subsides. Freaking awesome. I think this is the reason why I exercise so much (addicted?)-I'm rewarded for my efforts.
Any post exercise soreness now shows up about 48 hours after exercise and it lasts for a longer period of time. In my younger days it showed up the next day. Recovery from minor injuries take longer than they used to but I can usually just switch to another activity.
The bad news is that I flexibility is now much more of a problem. A huge problem. My ankles (achilles) are so stiff in the morning that I take shortened steps for the first few steps. This is in spite of stretching them out almost daily. My flexibility is much better than before I started karate. I'd hate to think what it would be like if I didn't work at it. Yoga would probably be ideal but it's not dynamic enough for me to keep interested.
Two years ago, at my first "black belt camp" several of us, both men and women, all about my age and all whom had started karate in their late 40's talked about what we notice about exercise and aging. Every single one of said "fear." We were all active in other sports but we just don't take the risks that we used to. It's not to say that we don't take any risks but I used to push the limits much more in my youth. As a corollary, we now compete against ourselves; we spend much less time comparing ourselves to others.
Life is so much better with physical activity but as SkiDiva said I'm preaching to the choir!"