the good old days, what does it mean?

Its when people remember old times.

Usually good experiencing.

its just an expression

Good Old Days Meaning

"The good old days" means the past, near or distant, when the speaker perceived times to be better than the present. (This is not necessarily true, just one person's perception.)

Example, In the good old days we didn't have any problems with gasoline prices; people used horses and carriages (and the streets were full of horse manure, travel took weeks rather than minutes and so on. Get the picture?).

People say it when they are thinking about their past. To me the good old days were the late 1990's when I was a small child.

When people think fondly about when they were younger. They only remember the good times; they forget all the bad times.