As everyone has said, the length of time can vary. I've not been very dedicated in my pole dance, and after 4 years, have only recently been seriously getting into aerial moves. However, if you know how your body works, you workout SMART as well as frequently, I would say that you could, potentially, achieve this within two or three years of consistent practice.
That said, I agree with the others; everyone has their strengths and weaknesses. It could take you four years to get the flexibility, but only one and a half to gain the strength. Or vice-versa. How your body is made, and what it's good at, will create a very special, specific and unique journey for you.