For most of my friends these days, "a life" is a wife and kids, but for some of them, it's just a house, or pets, or even a job.
Strangely, "a life" never stops them from having dinner with you or meeting for beers after work. It just stops them from doing anything that requires energy or planning. It's got to the point where I'm trying to figure out how to make new friends at an age where it doesn't happen by accident. But you find a guy whose Facebook page says "I love backpacking" and then you find out he hasn't done it once since he got married. I'm going out with women I'm not into just so I have somebody to do something with. I'd be too scared to get seriously involved with them, though, because then they would have a "life."