When is it safe to walk on a frozen lake?

[Gandalf]

Miles, walking does not constitute exercise, not for someone of your age.

Vigorous walking and I do walk at twice the speed of pretty much any human being. I do 3 1/2 KM everyday. My walking is like a 45 year old running.

I think you'll find most averagely healthy 45 year olds can run much faster than your speed walking. Bloody hell mate 45 ain't old and yet you go on as though being 31 is like middle age or something.

Probably, but I am doing enough to stimulate my heart and get some exercise. It's better than the nothing that most people do. I walk around the lake, I listen to some music and I enjoy it.

I do walk extremely quickly too, I have arguably the longest legs in the world and when they get going it is a little like a leg version of a Calzaghe combination. Windmills gliding over the floor. It is a glorious and mildly terrifying sight.