I did this earlier this year and it was great fun. If you're reasonably fit, shouldn't cause a problem as long as you have appropriate boots and carry plenty of water. Also make sure you have big plasters ready for when someone inevitably gets a blister on their foot. Wear thick socks to prevent this.
At a very steady comfortable pace (slow enough you don't really run out of breath), it takes about 10 hours. I think we did it in just over 8 and a bit and I thought it was too fast for me I was totally shattered afterwards. You gotta have a pint at the village afterwards too it'll be the best pint ever, well earned! :D
Edit: Actually, are you thinking of doing it in the winter? Could make it considerably more difficult. Slippy rocks, boggy paths (if they are still walkable at all), cold, dark etc etc.