You don't have a life when there's no diversity in your activities. You don't have a job, there's no social interactivies with family or friends etc. So, for example, this is how average your day looks like:
11.00AM - Breakfast
11.30AM - Gaming
14.00PM - Lunch
14.30PM - Going to the supermarket to get some food
15.00PM - Gaming, surfing the web etc.
18.00PM - Dinner
19.00PM - Gaming, surfing the web etc.
2AM - Sleep
You don't have a life when there's no diversity in your activities. You don't have a job, there's no social interactivies with family or friends etc. So, for example, this is how average your day looks like:
11.00AM - Breakfast
11.30AM - Gaming
14.00PM - Lunch
14.30PM - Going to the supermarket to get some food
15.00PM - Gaming, surfing the web etc.
18.00PM - Dinner
19.00PM - Gaming, surfing the web etc.
2AM - Sleep
I always saw "having a life" as doing something worthwhile and productive with your time, which of course is subjective and means different things to everyone.
You shouldn't take the "get a life" comments too seriously imo. A lot of the people who tell others to "get a life" probably don't have one themselves. They just say it since it makes people assume they do have a life if they're telling others to do it.
Being happy is the most important thing.
Personally, I do have a big social life atm since I'm at uni, and I usually go clubbing 3 times a week on average. But there were times in the past when I was working full-time and didn't have a social life, but that's just the way life goes. If you're happy like that then just go with it, although I do think it's good to have SOME social life, especially when you're young, since when you get older you could look back at the past with regrets and think you missed out on things which you can't do when you're old.