I'm 68 and I use metric (although I can use both) for everything. We do everything in metric in Britain today. I started teaching metric in primary school in Britain 1972!! So the Imperial system went out with the British Empire.
When will Duo get up to date? It's very frustrating.
It varies a lot. I went to school in the 80s and we were taught both. Our maths textbooks were ancient and in imperial and our headmaster was a mathematician who considered an over-reliance on base 10 was not a good mathematical grounding and demonstrated that the two systems work better in different situations. So I use both, I cook in imperial but am a scientist and only use SI at work.