STICK WITH IT....the first time I attempted "aerobic" movement, I had to run up and down my 6 stairs in my apartment...and managed a full MINUTE. After 3 weeks, I progressed to "around the block" and could barely walk that ....mind you, I was 21 years old!!!
in several months, I was able to jog 15 miles at a time....
Read some good books (and the posts here) about making sure to take it slow, wear the right shoes....and remember that mileage is not as important as simply getting out there and staying out there to remain healthy.
Thoreau said, 'A man is rich in proportion to the things he can leave alone.'