You are going to be amazed at how much faster the body get used to a completely different workout (like running) as long as you "learn" to like it, to love it, and to WANT IT SO BAD you can taste it.
I wanted to finish a 10K so so so so bad, for years! Now I want a half marathon!! I have finally accomplished a few 10Ks and realized I can move on to something else.
However, I am still planning on taking small steps, like you and Mary are. We cannot afford to get hurt by trying to run 6 miles every darned time we hit the pavement!!!! We are not there yet and therefore we have to pace ourselves. But we gotta do it.