Well Aly, what are your goals? Are you enticed by distance events... or are you more interested in saying, "I can run x miles at x pace". ????
I took my friend (relatively healthy girl) from sofa to marathon in 7 months. I had her do a walk/run combo... and at the marathon we did a 10 minute walk/3 minute run. We finished in 5:45. Which is a nice pace considering how much we walked it.
You can up your distances quicker if you do a walk/run and avoid injury. She had a couple of issues along the way, but nothing that didn't resolve itself quickly- and really those happened because she was just running/walking when she felt like- thus running too much. So I got her to stick to a timed interval and it worked out well.
I know for me... I have changed my calendar some for the end of the year... because I have been able to run a pretty decent speed, without walking... and I want to focus on RUNNING a half marathon- to see if I can crush my other half mary times. I have yet to run a full half mary. Maybe I'll do it injury free this year?
So, you can go either way... it's all about your personal goals.
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather, to skid in broadside thoroughly used-up, totally worn out, and loudly proclaiming: WOW WHAT A RIDE!!!!"