When calculating the stats on, say, January 1st 2024, and using a group age of, say, between 20 and 24 years, we were considering that everyone born between 2000 and 2004 had between 20 and 24 years. This wasn't accurate, since most people born in 2004 would have 19 years at that point, and most people born in 1999 would have 24 years.