Six feet is a BIG Ball Python. They are the exception. Most are between 4'-5'. My two adults that I have breeding are both right at 4'. The first year obviously yields the fastest growth, although they do continue to grow all their lives. I think most hit around 30"-40" by the end of the first year. 3 1/2' to 4' is normal for a two year old, of course, depending on the feeding schedule, rats vs. mice, health issues, etc. My snakes are all eating rats, so that is where my experience lies.