This is a really hard question to answer. Too many factors and variables involved.
As an example I think I got the most recent story;
I have been playing pool now for exactly 2 and a half year. Two and a half years ago I didnt really even know how to hold a cue, didnt even know what pool was but the little clips I would watch on ESPN when I was bored shifting the channels on my TV. I moved to the Raleigh NC area, right in the center of a bunch of pool halls and went to a pool hall played pool a couple of times and got recruited to play on the APA, so I started as a SL4 like everyone, quickly moved down to a SL3 but my competitive spirit just wanted me to get better so I did, by the end of the session I was a SL5. Pool was a hobby until a bunch of people told me that it was not possible for me to make it from SL3 to SL7 within a year, so of course I had to go a prove them wrong lol; which I did, and that was about the time I fell in love with the game so I kept trying to improve and get better. Yes, I have been putting a lot of hours every day into training, taking lessons, gambling, playing tournaments, playing league, watching matches, reading everything I could get my hands into, so pretty much pool is on my mind almost the whole day. Fast forward now I am a SL9 on APA. I am an A player in some tournaments, a B player in some others.
I live in an area where there are tons and tons of good players, the competition is pretty good, and there are many players out of state that come to play here.
I used to think it could be done, make it to a pro speed in the period of time. But now I am not so sure any more. At my best I have played pro speed (I broke and ran the whole set in a tournament match about a month ago race to 7), but the average game is not close to pro speed. I used to think I was close to it because I was misjudging my true playing ability, but at the end of the day the more that I practice, and the better I get the more I realize I am really far from playing consistently at that speed. Also, the better I get it takes me now twice as much work to get half as better than when I started. My goal now is to play the top players on the state without any weight in the next 2-2 1/2 years and not get murdered. So check up with me in 2 1/2 years lol.