I'm British. I live in the UK. I'm in my thirties.
I do a person's height in casual conversation (on forms I write it in metres) and driving distance in Imperial measurements (often; I use kilometres when I'm talking to someone I trust to know what a kilometre is, which is generally anyone under about 40). I do depth and altitude in metres, but sometimes I'll use an old chart that has feet (or sometimes fathoms, but that's the really, really old charts). Volume, mass, everything else is metric. I know my mass in kg. I've only the vaguest idea what a "stone" is. A pound? An ounce? Those are twee measurements I sometimes see in old books. I know how much a litre is. I don't even know what the metric unit of volume is. Cubic inches? That seems clumsy even for Imperial units. At the supermarket, the unit used on the fruit, veg and meat is kilogrammes. Last weekend I was comparing pork by cost per kilogramme. Which supermarket do you shop at that uses... I don't even know what you'd use. Not stones, I guess? Pounds and ounces? I remember at about age ten someone telling me the temperature in Fahrenheit, and having no idea whether that was hot or cold. I have less idea today of what it means.
Where this is going is that I thoroughly disagree.
Additional edits, for the fun of it:
"Though I bet you don't go to Asda and ask where you can find 2.272 litres of milk." Fair enough. I do buy milk in pints. If they switched to 2 litre bottles, I'd still buy it, and frankly I'd prefer it if they did. At the moment, I have to look at the scale on the side of the milk marked in litres to see how much I'm pouring into something (because the recipe I'm using specifies litres or millilitres; maybe there's a whole dual-industry for recipes in which you get Imperial units and I get metric; I note that the recipes on the BBC list both units; Jamie Oliver's web page is metric, Delia Smith is both, Hairy Bikers are metric, I've given up looking after those high-ranking four, but I note that not one of them is this Imperial only thing you talked about).
"Do you ever do mile-per-gallon approximations for your fuel economy?" Fair enough. I don't drive so this is a closed book to me.
"Do you ever buy a steak at a nice restaurant?" Yes, often. I have never once specified a mass the steak is to have. That it is marked on the menu in crazy measurements has always seemed a twee restaurant kind of thing; cosmetic rather than meaningful. The meat at the supermarket is, of course, in kg.
"Have you ever played golf or football?" Never golf, and football not since I was about ten. Perhaps we simply move in different circles. You're with the Imperials, I'm with the metrics.
"Where are you?" Deep south. Hampshire. As a drifting aside, I note that London is now approximately 40% non-British born, so that presumably means that about 40% of people living in London have even less grasp of Imperial measurements than I do. Perhaps metric is more common in the south.
Steak update: I am sure I have specified the steak by name, and its name is "Ten ounce" or "Eight ounce" or whatever. It is as meaningful to me as "Medium bowl of custard" or "large bowl of custard", for example. If you gave me a big bucket of sand and asked me to put about ten ounces of sand in a cup, I'd have no idea at all. I seem to recall that I once saw an ounce of butter and it was kind of about "this" big". I'd probably use that as a base.
Ramsay: A ha. Ramsay, of course, is Scottish. Maybe Scotland isn't metric.