Who is your oldest friend (i.e., the friend you have known the longest)? How often do you see or talk to each other? Do your close friends tend to stay the same year after year or change over time?
My oldest friend is also one of my best friends--his name is Mark. We met when we were four years old, on the first day of pre-school at our Catholic elementary school. We've stayed friends throughout all this time (we are now 22!) and even though we don't see each other often, when we do see each other, it's like no time has gone by at all.
That's what I think a real friend is--no matter how much time has passed, you're just able to pick up where you left off. You don't need to know every single detail of the person's life either; it's just this point of comfort and support that you reach.