It's easy for you to relate to your friends on most levels while you're all still in school. After that, lives tend to progress at various paces and they may take different directions.
Some of your friends will get married, some will have kids or choose not to, a few might take on their careers with full force while others play it safe or don't work at all. Of course there are still ways to relate to friends who aren't at the same place in their lives as you, but the differences certainly become more pronounced. What's the story with your group of friends?