I started walking, weight lifting and dieting in May of 2009. I began biking seriously in June 2009.
I began at age 46 and 294 pounds. Since that time I have walked probably 150 miles and I have biked well over 600 miles, mostly since late July.
This morning I weighed 253.
Our walk last night was cut short and we ended up doing 1.6 miles versus the normal 2.6. Hardly took a breath. Then I rode the bike 10 quick miles before dark.
My point is, I know exactly where you are coming from and what you are up against. You can do it and the advice you have gotten so far is spot-on. Just keep doing it.
The motivation for me is that I know I have to convince myself to do it, even when I don't want to. I always feel better for it afterward.
Keep it up!
Glenn