"Living with your parents is called childhood."
It depends on a lot of variables. That's a pretty over-generalized one-liner with plenty of unique situations to disprove it. When I got out of the military, my right leg was really messed up and I was undergoing treatment and was also hospitalized for a couple weeks. Does that mean that I regressed back into childhood? No, it doesn't. It means that I had just separated from the military, was injured, and needed to stay with my family for a while, no more, no less. There's nothing wrong, or childish/immature/slacker-like with that. In many cases, depending on the circumstances, it's indicative of someone being MORE of an adult (and more courageous) than most.
There's also a lot of people who have moved back in with their parents because of the economy. If you suddenly lost your job and couldn't pay your bills because you were broke, would you rather move back in with your family, or end up homeless? I think that's a no-brainer. And in these times people need to quit being so damn judgmental of others. There's a lot of people out there who have had some bad luck in the last few years, many of them through no fault of their own.
Now if he's talking about lazy bums who contribute nothing and spend all day playing video games and eating Cheetos, and do nothing to better their lives, then I agree. But like I said, it's a case by case thing. Making blanket statements is pretty unnecessary, plus they're rarely, if ever, correct. It only takes one instance of something not being true to make it untrue.