4k: My first ever play was a 4* S rank, but I had prior experience beforehand (Robeats), I think it took me about 2 years for 4* S? 5* S was a bit trickier, it took a few weeks after I got my first 4* S. Got hard stuck at 5* for a really long time because I never pushed for 6 stars. Soon after, I pushed my boundary. 6* was galaxy collapse, it took days of training but I eventually got it around 3.5 years of playing. 7* had taken me more than 4 years, on parallel universe with halftime (I am an LN main). Nearing 5 years of playing, I got S on HALL very recently...
7k: I actually started learning 7k on Osu, it took about a week to get my first 2* S. 3* took about an entire month. I only have 1 ever 4* S which was set last month.