That's what I said, more or less, to go a little further, starting at high school, you and your friends have a lot in common, just off position in life, high school students, then everyone starts getting cars, and depending on what path you took in high school, things become a little more defined. For me, it was smoking blunts, selling weed, among other drugs, hustling with your friend for hours at a time, spending like 5 hours in a car. Then, drinking, parties, drugs at night. So, you live a life, very similar to your close friends at that time. None of you want to be at home, you are all trying to get girls, stay out of parental trouble, everyone has more in common.
By now, 27, 25, whatever, people are doing different things. Some friends have kids, some drink/drug still, some are married, some haven't changed, so, my friends and I are still 100, but it's based more on shared experiences, and 10 years of friendship, rather then that we spend all, or a lot of our free time together. My closest friend, I'm not going to hit him up to go to Nordstrom and Gucci, or go to a movie, because it's not his thing, Same way he won't hit me to drink all day, and go to a sports bar or some shyt on Sunday for a Chargers game, cuz that's not me. But, we are still friends. I don't really have casual friends, so I am on my own most of the time, I almost prefer it, but it can be isolating.