Hi Tabary,
Trading as a subject to be learned is conceptually no different to learning anything, say, how to play the piano: you can study and practise yourself (there is a lot of material out there); and/or you can find an experienced and knowledgeable teacher to help you learn. A good teacher should help you get there better and more quickly but you can certainly do it yourself. That said, trading is a funny business in that so much depends on your emotional and psychological makeup, you'll need to honestly evaluate yourself as you go along to understand if you really have what it takes in that regard.

As to how long it takes, it's a bit like asking how long is a piece of string? It'll take as long as it takes depending on your aptitude for the task, ability to learn from your experiences, and effort put in. But I'd look to measure it in years rather than months, just like learning to play the piano well.