Lots of good stuff here, and you have my sympathy.
I have helped a lot of younger folks get promoted. Both people who worked for me and just people I was around. Here's the advice I gave:
1. Check the job descriptions, if your company has them. Look at what your current responsibilities are, and what are required for the next step up.
2. If you are doing the "next step up", bring that to your boss's attention. If you aren't, ask "what else do I need to do to get from point A to point B".
This often works.
For the weaker employees, they aren't able to do the "next steps" satisfactorily.
For the stronger employees - sometimes they were already doing it, and got promoted immediately. Sometimes they were able to add a couple of new things and get promoted.
For some timid employees, they don't even ask, because "my boss is just going to say that this job entails X, and there is no place to move up". (If that is true, then find a new job.)
But this very much depends on your boss and organization, as you have found out.
For myself, I was a top performer. I struggled to get promoted at my last job.
Boss #1: Well, let's think about this a little bit, you are doing everything on the next step up except this ONE THING. (which didn't apply to my job). 6 months later, Boss #1 leaves.
Boss #2: Technically, this was my (new) boss's boss, during our annual review - done over the phone because he was in a different state. "Wait, why are you a 3, your job is clearly a level 4, I am going to get you promoted". Boss #2 leaves a month later to get a new position.
Boss #3: My actual boss from above, after he's got 6 months under his belt, submits a request to his (now new) boss for a promotion.
Boss #4: see, they end up closing down our group and restructuring, so my immediate supervisor (#3) gets a new boss. So I go up a level (to the new VP, who is 2 levels above boss #3). He says "well, why does the title matter?" "Because I've been doing the job for 2 years and it affects my compensation". "Well, this shouldn't be an issue." Which is a nice way of saying "no promises".
So I left to go to a new company.
Over the years here (almost 7), I've had really good and really bad bosses.
The bad ones tell you your ideas are stupid in meetings, and then 2 weeks later have this "great" idea. Or they make you miserable.
The mediocre ones are either uninterested or inexperienced when it comes to developing employees. We have several of them, who go with "status quo" and just aren't comfortable advocating for their employees when it comes to promotion, giving more responsibility, etc. And we don't have job descriptions or levels here, and I think that's on purpose.
The good ones actually know how to motivate you (with or without money), train you to do new things and take on more responsibility, and advocate for you in the company. I have had two of those. So awesome. And I like to think that I was that kind of boss when I managed 6 people. I think most of my employees would agree. However, upper management would not necessarily agree - apparently advocating for your people is great if you are a man, but is seen differently if you are a woman. Who knew.
But I've also had the bad ones. So I had about 3 good years of raises and promotions, then got a new boss through restructuring. And he was awful. I'd never found that glass ceiling before.
He's gone now, but the detritus remains. We've had 3 rounds of layoffs. I am no longer a manager, as we've basically laid off all of the junior employees. I guess I'm lucky to have a job, or so that's what we are supposed to think.
You have a bad boss, I'm very sorry. If I were you, I'd speak with your boss again, and maybe go to his boss if necessary, depending on how big the company is. Your point about other people getting promoted is TOTALLY VALID, I understand that. BUT the way that you need to frame it is to completely ignore that - you simply have to point out that your role and responsibilities are "X", and have been for "X" amount of time, so clearly you should be classified as "X".
Good places care about developing employees, but in the end, it's up to you to make that happen. If it's not happening where you are, look elsewhere.