I know what that's like, too! I'm 16 as well, and in a very similar situation honestly. I had a bunch of old friends through Minecraft that used to play, now none of them play anymore (or they ignore me because they're being drama queens for no reason, lmao) and I haven't really been able to play with people on there since I stopped for about 6 or so months at one point when I'd gotten bored with it.
I can also say that there are many others around the age of 16, slightly younger and older, who still play, too, though! I kinda know a group of people on the server I'm usually on, and they're all between 14-22/21, can't quite remember the oldest one's age. And about a year ago there was a similar group of 16 and 17 year olds I saw a lot, but they've disappeared for all I know.
The most interaction I have with people in Minecraft only happens when I'm playing the game with my younger brother now tbh, and he doesn't play much since he got bored of Minecraft at least a year before I originally did.
There's definitely many people in this age range who still play and/or feel like this, you'd just never know because most of the ones I know, myself included, pretty much never talk in the chat so you don't know a thing about them since they're not looking to discord or whatever with someone for the same reason that it's all kids much younger than them most of the time. I guess I wouldn't really know since I've never touched discord in my life, but Minecraft is still mostly younger kids no matter what anyone says, lol.
One thing I've noticed as far as age groups go with Minecraft, is different things have different age groups that generally are around it. Like, I can say without a doubt that Lobby 1 on Mineplex is not only the weird place where OG names decide to sit afk for hours on end for some reason, but a lot of people around the age of 16 are there, too. And, still Mineplex since that's the only thing I play anymore, back before the screwed over the Arcade games and Death Tag was still a stand alone game, there were tons of people around the age of 16 there, some quite a bit older who played the game literally every day. I'd know because I was one of those people, and it was great while it lasted ;w; After it pretty much went down, the community there died, but I can still find like fragments of the main group of people who played it throughout the lobbies waiting for a singular damn game of the thing to show up since it's like never there
And about people who think the game is childish; even if the game is mostly full of younger kids, it doesn't mean it was still meant for all ages anyhow. Like the Minecraft YouTubers back in the day when YouTube was great, they made their living off of it, as well as genuinely enjoying the game. Until most got bored and either stopped or legit disappeared off the face of the internet?? Even if the golden age of MC is pretty much gone now with it's biggest names no longer around or playing the game, it's still a hella huge community full of exactly what it's meant for; a large range of ages who just want to play a silly game because it's fun.
Oh boy, I ramble a lot, aah, sorry if you actually read all that nonsense QwQ