The Wave by Algernon Blackwood

The particular moment when this happened, suitable, too, in a chance, odd way, was upon a mountain ridge in winter, a level platform of icy snow to which he had climbed with some hotel acquaintances on a ski-ing expedition. It was on the Polish side of the Hohe Tatra.

Why, at this special moment, pausing for breath and admiring the immense wintry scene about him, he should have realised that he reached a similar position in his life, is hard to say. There is always a particular moment when big changes claim attention. They have been coming slowly; but at a given moment they announce themselves. Tom associated that icy ridge above Zakopane with a pause in the rushing of the years: 'I'm getting on towards middle age; the first swift climb -- impetuous youth -- lies now behind me. The physical parallel doubtless suggested it; he had felt his legs and wind a trifle less willing, perhaps; there was still a steep, laborious slope of snow beyond; he discovered that he was no longer twenty-five.