This varied by sex, with the population of males aged 20 to 34 years old decreasing by 9.8%, while the population of females decreased by 3.7% in mid-2021.
Roedd gostyngiad o 9.8% yn y boblogaeth o wrywod 20 i 34 oed, tra bod gostyngiad o 3.7% yn y boblogaeth o fenywod yng nghanol 2021.