Yes, I have a life.
I have great friends and a good job. I go out often, sometimes to parties, sometimes just cause. I travel overseas frequently, and I have friends in many different countries. I do not have a girlfriend, though that is because I haven't met a person I want to make my girlfriend.
Saying 'Get a life' is pathetic. I will counter with this quote: "I'm a gamer, I have many lives (Though currently I've only got three left, stop annoying me)"
Honestly, your brother has no life. If he is looking at online threads and saying how little of a life everyone there has, he needs to go out, meet some people, and ask them if any of them play games. 90% will say yes. If he thinks only people with no lives play games, then he obviously has not had a life for the last 6 years AT LEAST, and needs to get out and socialise more.
Might I also point out, what is 'a life' I am living, therefore I have a life. What else do I need to do to have a life? By learning C++ and python, and doing generally nerdy stuff, I set myself up for a job in the IT industry - jobs that can pay very well at times.
People like your brother need to get out of the mentality that games = bad. The majority of people I have met online have jobs, friends, a girlfriend, sometimes families - tell me they don't have a life.
"Get a life" is a stupid phrase used by those with a need to justify what they do with their life to themselves as they are more than a little insecure about what people think about them. The irony? Those that just live their life, and accept the way others live their lives are almost universally respected in turn. I don't drink, something that 99% of people I know do. They respect that. I don't try to stop them drinking, they don't force me to drink, and each of us just ends up respecting the other more.
If your brother feels the need to belittle others he does not even know simply because of what he believe they do with their life, and that he believes that that is the wrong thing for them to do with their life, he really needs to 'get a life' himself, and stop worrying about what others do, and more about how he can make his own life more enjoyable.