I am also the wrong side of 50 and the wrong side of 11 stone 
I started the NHS couch to 5k a few weeks ago. Did weeks 1 to nearly three, then came down with a stonker of a cold for a week. Started week three again, only to turn my knee at karate, resulting in another week off. (Maybe the fates were trying to tell me something!)
Just started week three again this week, dragging along my 12 year old son and have now completed that, so will begin week 4 at the weekend.
A couple of things I noted- it took me nearly 3 weeks to work out how to run properly
By this I mean how to to work out what was comfortable with footfall, and when to breathe.
I chose Sarah Millican as my commentator because I like her anyway, but also because previous efforts have been commentated by personal trainer types and I found them irritating.
Other than that, the crucial thing I found was not to attempt to fly along, gazelle-like, but rather plod along more like a ponderous elephant. I'm aiming for the time first, I'll work the speed up later.