In reply to Voltemands:
> C) Standard sort of time for a mid twenties, regular road runner who gets out a few times a week running 5k to 10K per session.
This was almost my sort of situation when (many years ago) I did my first half. The longest I'd run before doing it was 7.5 miles but I was running maybe up to 3 times a week (so long ago I can't remember). I did it in just under 1:35 but it knackered my arches for a little while because I wasn't wearing proper running shoes; Adidas Sambas were ok for shorter distances but not 13.1 miles
As soon as I stopped the pain set in and I limped/shuffled home from the finish.
So I think a reasonably fit 25 year old man who runs maybe 3 or 4 times a week should be aiming for a first half-marathon time under 1:45 - that's 8 min/mile pace which is not particularly fast. A similar woman should probably be aiming for sub 2 hours.
A good rule of thumb I read about was to work out your average daily mileage and then multiply that by 3 to get your comfortable race distance. So for a half-marathon you need to have built up to about 30 miles/week. I never really got above 25-30 miles/week but all my (few) halves were between 1:28 & 1:35 and in one of those I was beaten by somebody pushing his kid round in a buggy!!! - overtaken going up a hill !!! - so I wasn't particularly fast.