Since I don't run, I can't really offer any suggestions or help about it. The main thing I could say would be make sure your shoes are the best you can afford and then some, because when people are out of shape, it's easier to get an injury which could sideline you for a long time. That, and to take it slow. Resting in between runs might be the best thing, so you don't overdo it. As you said, maybe a brisk walk every other day to keep moving.
There are others here whoo can comment on the P90X - I've never done that program or Cross Fit. I just don't want the intensity of those types of workouts anymore. I tried the "Body Combat" Or Bootcamp type workouts and I don't wanna workout that hard anymore.
But! I will be 57 in May, and I've done some form of aerobic dance & cardio exercise for the last 40 years. I also rode a "real" bike up to 10 miles a day when I was a stay at home mom - but I had time to do that. Now, I don't. I always found something I liked to do and just kept doing it to keep active.
I joined the gym here in PF when I moved up to Maryland, and have been doing spin classes since then and I also did cardio weight lifting class ("Body Pump") for about 5 years. I was having problems with "tennis elbow" and some issues with my shoulder when I took up golf, so I had to stop the Body Pump a little over a year ago, (and golf, too) because everything aggravated that arm. I took up Yoga and 7 months later - I have virtually lost the pain in those two locations.
I guess my point is - if you find the jogging to be too much in whatever way - just change over to doing something else. Walking briskly may not be the same as jogging, but you can burn a lot of calories and get a lot of cardio benefits from doing it. Or even a spin class. (after you get used to that seat - you've got it down - and you will get cardio benefits!)
Whatever you do, don't quit! 
