DP and I are in our mid-60s. We lived in the EU for many years and ended up thinking about almost everything in metric. The hardest things to switch to were people's heights and (especially) weights. Even after getting a bathroom scale in kilos we would talk about people weighing 10 stone, 12 stone, etc. But otherwise we're metric all the time. I haven't used the "inches" side of a tape measure since the 1980s.
Nowadays it feels strange if we're around Americans and have to translate Celsius temperatures to Fahrenheit for them, or convert 100 metres into 328 feet. (Americans use feet, not yards, for most distances less than a mile. They only seem to use yards for gridiron football.) And don't get me started on "ounces" as a measure of liquids and not weight.
But... I still say "couple of inches" or "about a foot" for short distances, to the dismay of our DC who grew up 100% metric in France, and I can still envisage 4 ounces of flour in a dual metric/imperial recipe or a pound of onions at the shop. I don't think these things ever quite leave you.