Old people are frail. The world appears frail to them. And as you age, the flaws of the world become more apparent, and the world appears even more like it is hanging on an edge.

Of course most people also have rosy glasses about their good old days, where people followed the law and things just worked.

So old people think adhering to rules and avoiding chaos is what kept everything from falling apart.

Also, as you get older, your routine becomes everything, as your neuroplasticity decreases and ability to deal with change. Rules keep things the same.

EDIT:

Also, one of my favorite explanations of popular vs nerd people in high school: popular kids spend all their free time being popular. Nerds work on school and other things.

In that vein, old people don't really have anything to do other than be nosy. They sleep less, are retired, and living off social security means "hanging around where you're at and not doing much".

They are perversely like teenagers.