I'm a child of the 80s from a scientific family. Which meant I grew up with everything in metric, except for the countless things that Brits delight in measuring in their own archaic units for ease of obfuscation. Distances in Kilometres, speeds in mph. Height of doorways in mm, height of people in feet. Feet in barleycorns, whatever the fuck they are. Plastic money for maths lessons in "New Pence"[1], cost of things in shops in "Pence". That sort of thing.
At some point I decided it was better to have a feel for what a unit was than to be good at converting between them, so gave up trying to make sense of old people and Americans, except in contexts worth resorting to arithmetic (much like reading alanlgue clocks, really, which I never found reason to become fluent at). Inches and feet get divided by three. If someone has a baby (everyone's having a baby) I need to convert to metric and look it up on the percentile chart before it means anything to me. I've no idea what a gallon is, other than that it's likely to be the wrong kind of gallon, but I can estimate the volume of a bag in litres. 'Mil's are a point of much contention, because they're a unit I can't avoid and my brain will treat them as a synonym for millimetres in some contexts, which is a recipe for Mars Climate Orbiter type disasters.
Fuel consumption, like the gain of bone-conduction hearing aids, should of course be measured in m2. Unless it's an electric vehicle, when it should be measured in Newtons. I have a good intuitive sense of what a square metre and a newton are, I've no idea what a mpg looks like.
[1] At no point did the teachers or the workbook authors consider that as the generation who'd never known anything but metric money we might benefit from some explanatory context for that ubiquitous wording.