First of all, don't worry about it. You are a programmer the moment you start writing code.
I've been doing front-end development for 13 years now (10 years as a hobby and 3 professionally) and I still have days where I wonder if I'm the imposter in the room.
What I find helps a ton is talking to people. Ask questions and get answers. Have people ask you questions and you answer. What this does is establish a knowledge transfer and helps level the playing field.
No one is an expert at everything. Even the most skilled developers Google the most abstract things. Yes, people still look up how to make an unordered list in HTML.
So, reiterating, don't worry about it. Even starting out, there's a chance you know something someone doesn't. That is your treasure if you seek it.
Adding to that, my take on seniority is you're a senior when you look at bad code and it hurts you on a spiritual level and it compels you to fix it.
It's the itch that can only be scratched by making it go away.
I'd say: When you can resist that urge... then you're a senior.
TLDR: You are a programmer when you program.
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