That was such a nightmare. We had an NCO team of 5 Cpls on sqn at the time, and then almost over night that became 4 Sgts and 1 Cpl because we all turned 18 at a similar age. People were promoted just to keep them in.
Back then, cadets on our sqn usually didnt get to Cpl until they were around 17 years old (remembering CWOs could stay until 22nd birthday) so there were some very quick progressions - I’d only got Cpl at 17 and 9 months.