Less than 3-4 years is absolutely junior dev. Up until around 7 or 8 years is mid-level. Passing beyond that would be senior dev and the other titles then follow.
With the obvious note that it's not strictly time bound - someone could easily get stuck at mid level for much longer if they aren't progressing. It's pretty hard to still be only junior after 7+ years
I still very much consider myself junior but someone I know with less experience than me just recently got a job with "senior" in the title. I have seen senior job postings that say something like "3+ years of experience."
I absolutely do not consider myself senior and I don't think I will for at least seven more years.
I don't personally think it's strictly about the time one's been programming, although in my experience that can be a good benchmark for e.g. how good one's abstraction, API design, etc. skills are.
If there was a required reading list for professional developers, I would put her work on with zero hesitation, I feel it to be that important.