> It couldn't possibly be because he's older... was taught imperial when he was in school... and humans tend to go with what they know?
I was born the same year as him and we were all taught metric units in England from the beginning of school, imperial units were never used. We were introduced to it in passing when we were aged about 8 or 9 as a funny old system that people used to use so we might come across from our older relatives it but not something we should pay very much attention to . Britain in the late 60s early 70s was still optimistic and looking to a scientific new future, white heat of technology and all that, and metric measurement was seen as part of the scientific new future (remember we had decimalisation of our currency at the same time, 1971, so we'd moved to 100 pennies to the pound from 12 pennies to the shilling, twenty shillings to the pound: imperial units were out of fashion). Metric measurement was pretty well known even by our parents at the time who'd gone to school in Imperial times (literally: pre 1947 when India, Pakistan and Burma were part of the empire, run from London) and taken for granted.
Of course I should be fair and note that according to wikipedia, DC went to an exclusive private school from the age of seven so perhaps they had rum ideas about education and believe the empire was about to return and taught the kids a dead measurement system... but if it followed the national guidance on curriculum, he would have learnt metric.
We still have a passing knowledge of imperial units in the UK, folk still know a handful, but it's a very partial and incomplete understanding and the majority of people under 50 would look at you as being a bit crazy if you said you wanted them to work in pounds and ounces and feet and inches. Most of them wouldn't know how many pounds were in a hundredweight or feet in a furlong.
DC is trying to out UKIP the UKIP and gain favour with the over 60s Little Englander vote.