I think it doesn’t matter if you fulfill any objective criteria of being fit, it depends on what your goal is. For example my short term goal endurance-wise is climbing Mont Blanc via the Gouter Route in one push from Tete Rousse. Which looks like it will give or take be about 1700m of elevation gain and loss in a day. So for me to be fit, I have to go up and down the hills here in my home town and get to a bit more than 1700m with a bit heavier pack than I will on the summit day, to have some margin.
But for other goals they would need less or more than that.