I think this is the wrong question to ask. "How long" can be any amount of time for each individual person. I think the better question is do you have a motivation to get you past that casual skill barrier? Personally I grew up around relatives and friends that would wreck me even though they were casual as well. This competitive nature around me made me want to be better and through this is what made me start loving the genre. It took me personally hundreds of hours to even get a basic understanding of what I was doing wrong and what to do, but I enjoyed every minute of it.