In reply to Joemanglerocks:
Did it when I was 18 in much the manner you describe although I took ten days and was pretty rough when I finished, however being heavily steeped in the DofE way of doing things I seemed to bring more or less everything but the kitchen sink with me (in a large green rucksack).
A few comments if I may...
Firstly, being able to walk 30 miles in a day is one thing. Being able to do it again the next day...and the next...and the next...is quite another. It's also worth bearing in mind that the final Commando test for the Royal Marines is a 30 mile route march in 8 hours. Not easy, 30 miles.
Secondly, besides the practicalities of eating and sleeping, you will want to consider how much water you can carry with you and when you can replenish it. A litre of water weighs a kilo but it doesn't take many bottles before it starts to feel like a real dead weight.
Similar to the above, being 'mountain fit' is a different sort of fitness to being 'running fit'. Especially if you plan on carrying much weight. Practise walking with a light load then increase it as you are able. Condition your legs and back to help with the increased demands you'll be placing on them. Finally, look after your ankles. Do some balance work and strengthen them as a twisted or rolled ankle at any stage on that walk would seriously spoil your day.
Hope that helps!
All the best and hope you enjoy it!