Bit late coming to the posts on this thing but just had to say that as a very nearly 50yo asthmatic with a dodgy knee, I'm really proud to have got this far.
it is only with the encouragement of my girlfriend (who started this programme 5 weeks before me and is moving on to greater distances) and peoples posts on this site.
As for encouragement for others all i can say is that everyone has their own reasons to start and you have to keep those in mind to give you the fortitude to make it through to the end. And it really doesn't matter how many times you have to repeat or re-start, so long as you don't give up on your reasons.
Have fun everyone....