In reply to Big Z: Just did it last week, except we went over Robinsons and down Newlands valley for Buttermere to Keswick.
Start feels a bit contrived, but some good days walking and Boot to Buttermere is the best and toughest day, in my opinion.
The basic route is very steady and my mid 60's in-laws both managed it without issue. Overall, a good way to spend a week in the Lakes.