“Half one” is archaic English, and common German, for 12:30. Similarly “my 27th year” just sounds archaic to me: I wonder if you went through a bunch of 19th century writing if you’d see ages more often be “Xth year” vs “X-1 years old”.
There may be something cultural that caused such a shift, like a change in how math or reading is taught (or even that it’s nearly universally taught, which changes how we think and speak because now a sizeable chunk of the population thinks in visually written words rather than sounds).
Isn’t “half one” used as a short form of “half past one” these days, I.e. 01:30? That has been a source of confusion for someone used to the Germanic way.
I had this exact topic with an Irish coworker who lives in Germany and has issues to convey the right time. For me as a German „half one“ is half of one so 12:30. Same for „Dreiviertel eins“ -> „threequarter one“ being 12:45 and „Viertel eins“ -> „quarter one“ being 12:15.
To be fair the logic behind this is also under constant confusion as some parts of Germany rather use „viertel vor“ or „viertel nach“ -> „quarter to“ „quarter after“ and have no understanding of the three quarter business.
There may be something cultural that caused such a shift, like a change in how math or reading is taught (or even that it’s nearly universally taught, which changes how we think and speak because now a sizeable chunk of the population thinks in visually written words rather than sounds).