Why are you assuming young people don't live with old people? It's extremely common.
https://ec.europa.eu/eurostat/documents/3433488/5579620/KS-S...
Looking at this data for the US, it could be a factor for COVID mortality being higher in minorities:
https://www.pewsocialtrends.org/2010/03/18/the-return-of-the...
The numbers you cite are explained by old people living in retirement facilities or coliving arrangements, but that doesn't imply cohabitation with young people. Under these circumstances, special precautions can and must be taken.