Well, there is the rather obvious problem with that theory -- namely it's untestable and therefore not science. We can't exactly go out side the universe to see if there's some pimple-face kid running a simulation. So it makes the entire question silly on that level.

As far as whether other civilisations would run a simulation -- we do, to a point. We run weather, we run geographical simulations, hell, we run MMORPGs stuffed to the gills with AI. It's certainly possible, in fact it's likely. How many COD and Elder Scrolls games are there each populated by thousands of AI characters and existing for the purpose of entertaining one singular non-AI character controlled by a player in a world created by another party. Maybe the PC will show up for milk and cookies. But as it stands, it's impossible to tell him from another one of us, or know if this is a simulation.