I have worn leather trousers (for gardening) for many years. What I will say is that the leather trousers I wore at 35 still fit my aging (almost 65) thighs (hips and arse). Everytime I zip up gives me a moment of delight...although this is probably due to the flexible nature of old leather rather than viciously intolerant denim or canvas. Moleskins and, to a lesser extent, corduroy (my summer work choices) have a similar forgiving effect. I have 3 pairs of leathers, all soft, lined and after many years of wear, completely lovely. I may have to attempt a photo. They do not smell, either, despite regular rucking in soil. I treat them like my wool jumpers...that is, never washed but allowed to air on the washing line on frosty nights.
Lycra will NEVER be worn though. Or shorts.