Hi! I used to learn Mandarin Chinese. I did it for no more than 4 months. I have to tell you that I didn´t have a teacher, it was all by myself. And that was a mistake. I had native speakers who helped me. But that is not enough. However, I reached an interesting level in just some months. I think it was because I used to take time to learn everyday. And also, because some methods I used.

It will be strange at first but if you put the time needed to learn it, are committed to improve and (this is important) have a teacher, you´ll see improvements. 

So, I recommend that you: 

* Find a teacher (if there aren´t mandarin chinese teachers where you live, try on italki).

* Focus on pronunciation ( It is very important if you want to be understood).

* Use a way to remember characters like writing them down on a piece of paper (don´t try to just memorise them, it´s not a good idea).

* Find other chinese learners (It will make things easier to share your achievements and have someone in who you can count in bad days) 

And last but not least:

* Have fun (Try to make learning interesting by talking to chinese people, watching chinese music videos and things like that).

The last one is very important for me because it is the basis of whichever language learning. Do what you like. If you like reading, read. If you like watching movies in chinese, do it. If you don´t find your learning interesting or you don´t REALLY like what you do, you´ll end up quitting. 

Good Luck in your learning. And don´t forget: Focus on the way, not on the end of it.

     A lifetime for sure. However, in speaking of concrete terms you could gauge language proficiency through the level you reach on the HSK. For me it took 3.5 years of studying (basically no time in China) to reach the HSK 6. I would argue that based on how hard you work, you could reach that proficiency level in less time if you were in China, more or less if you are not in China.

     With this level I would feel comfortable or at least be able to adapt to various professional and academic environments, linguistically speaking.

     For a path to "fluency" in the sense of being able to have detailed and intellectual conversations, I would put emphasis on learning to read because this will broaden your intellectual horizon in the Chinese speaking world. Of course, practicing speaking is a must, but you cannot reach fluency (intellectually speaking) just from speaking with Chinese people. The depth of conversation you have with others will never reach the depth of a well written article or book.

    To summarize, you could develop language skills with a strong foundation in approximately 4 years or less. Probably less. For mechanical fluency, or the ability to talk at a fluent pace that sounds semi-natural, focus on speaking with others on whatever topic. For intellectual fluency, or the ability to discuss a range of topics in depth, focus on reading or watching news/documentaries/interviews and applying that knowledge in discussion.

@William Fisher

William 这个人跟你聊了一次以后，会完全无视你的存在，我不知道为什么他是这样的人，我觉得很奇怪！

I just don't understand why you didn't even bother to reply my msg no matter it's on skype or on italki. Did I do anything wrong? I thought we had a nice conversation. What you did later on really makes me feel you are not a nice person.