Alright Personal, I'm turning to you for help. My friend, we'll reference her to A, she thinks that another friend, we'll reference her as B, is starting to drift away. A is starting to doubt her friendship with B, because B has started to hang with older people and is constantly pushing A away. A is crying now, because of how B has drifted away. A texted B about how she thinks their friendship was falling apart. B only replied saying that they were growing up, and then said she was busy with other things and didn't want to talk about this right now, and said nothing more than a simple "bye". Now A turned to me for help, but I just didn't know how to answer. B was my friend as well, but last year she started hanging with the more popular people and drifted away. A was friends with B for 4 years, I, only 1. So, Personal, I need suggestions/opinions on this. Anyone have any?

From what it sounds like, it seems "B" is trying to grow up. From her point of view, that means hanging out with the older crowd, trying to get known.
Sadly, this is often a short term plan, and usually doesn't work.
Still, there's the problem of "A."
One of two things will happen.
1) B will end up with friends who treat her poorly because of her age, and will eventually come back to A. She might not have anyone to turn to when all her new friends are the source of a misfortune.
2) B wants to hang out with older people (probably for appearances), and won't go back. Unfortunately, that's her choice. Still, at some point, she may just want to talk every now and then. Still, A needs to respect her friend's decision. She shouldn't be spiteful, but rather, understanding. If she hasn't moved away a great distance, then the two are bound to talk every now and then. It's not like losing a friend entirely, but rather, becoming less close.
It's still a bad feeling, but these things happen.

I think >>2 is mostly right in his/her comment. B really does go out of her way to act older and more mature. The problem is, however, that she isn't old or mature. Trying to be more mature is a sign of childhood. And here's another problem: even if you tell B that, she won't react, because people like that are quite stubborn. As to what can be done by you, that's a tricky question. You cannot really be of much help to A, but you can be a valuable friend. And that's something A needs in this situation. But there's a few outcomes, as stated by Black. In my opinion these are the most viable: Either A starts hanging out with B's crowd (which has a high chance of failure), or A forgets about be (at least for the time being), and turns to you. I'd suggest trying to get A to do the latter, because no-one knows how the first scenario will turn out, and you seem like a reliable person and friend, something A can't do without. I hope you guys can resolve this, best of luck.

Not gonna lie, it hurt my brain to try and follow that o~o