I would second that, not super fit, just a regular walker. I did the round a couple of years ago for the first (and probably only) time as part of getting a bit fitter before doing the Pennine Way.
The worst bit, as Sarah says, is the long bit at the end; I remember sitting at the top of Ingleborough being told the car was still 5 miles away, and thinking there was no way I could get there. However, not having a choice.... then in the last couple of miles people started running past me to get in under the 12 hours, just to rub in how pathetic I was being.