I learned 3X3 actively for about a year,
1 month to solve sub 1 minute
2.5 months (1.5 months later) sub 45,
3.5 months sub 40 (learned F2L)
4 months sub 35 (learned 2 look OLL/PLL)
5 months sub 30
9 months sub 20 (average ~19) (learned advanced F2L)
Didn't learn much else after that, but got more consistent. When I picked up learning 3X3 again almost 5 years later (yes I know...) I averaged about 26 seconds, took about a month to get back to 19 average, learned a few PLLs and almost yellow color neutral and now I average around 17-18 (about 2 months of practicing).
Truthfully, there is no normal rate of progression, since it depends how much time you have and how you practice. I started learning in high school and into COVID, so I had a decent amount of time to devote into cubing. It's a little harder for me now as an adult.