[PrimeMcFly]

> How would they do that if they don't have your address?

If you need to deal with taxes, you submit your address to the tax agency.

If you need to deal with license stuff, you deal with the equivalent of the DMV.

And so on.

There's no need to just file your address with the government 'in general'.

> a decent amount of elderly don't use the internet, how would they be contacted?

Internet is kind of irrelevant. Most government agencies don't use the internet to contact people unless they specifically opt in and the agency offers that.

They would use your last known address, or wait for you to contact them.