When I started learning Chinese, I was horrified to hear that it would take me 10 years to become fluent. 27 years later I'm still working at it. Due to my work on television, some Chinese language learners may consider me a role model of sorts, but every day I'm reminded of what I don't know and how much more there is to learn.
Who cares how long it takes? Just do it! If you really want to learn Chinese, you will devote yourself to it however long it takes.
Gaining fluency in Chinese is a difficult practice. All manner of things affect how long it will take, from time and dedication, classes you take, and finding a good teacher. Fluency has a different definition in most peoples minds, for the sake of this answer, I am going to consider fluency the ability to read and understand a newspaper, as well as engage in complex unscripted* conversation.