How long is a piece of string? :)
Impossible question to answer Erel. Depends on your circumstances and your motivation. Think how long it took you to speak English fluently as a child (and then you soaked up knowledge like a sponge!). I'm learning Spanish, and I've given myself 3 or 4 years, by which time I hope that I will be understood by natives and I will understand them. I don't expect to be fluent. I would suggest that you can't be fluent without spending some considerable time in the company of natives. :)