I did the British Heart Foundation 10k this past weekend, and after I finished that (not particularly well or fast), felt I needed a new goal to look forward to. I always imagined I would do the Royal Parks Half Marathon as my first, but that's a full year away, and I began my half marathon training (which should take 12 weeks) yesterday, so should be running the distance by Christmas.
I'm telling you this, particularly if you are just beginning the programme, because the Brighton Half will be just 50 weeks after I began C25K. I am 45 years old, and was 3 stone overweight when I started. That's what the programme can do for you. Keep going!