Vitamin D. Consider if you have dark skin you will have to supplement vitamin D because sun might not be good enough. This might actually explain some of the increased disease risks faced by darker skinned people but maybe not all of it. As far as the sedentary lifestyle, as a person ages they lose muscle mass every year so if you do not continue to build muscle you will become frail and weak in old age.
Of course there is testosterone replacement therapy or steroids but it's not a guarantee that your doctor will prescribe it as you become old.
I agree. You also have a decrease in stomach acid as you age. Adding a few fresh juices into your daily diet can help increase nutrient uptake in the body. And by juices I mean juicing fresh vegetable and fruit at home with a high quality juicing machine.