I think it depends on how frequently you trade. For me I would say I traded on a daily basis with a demo account for about 1 year, then traded with a live account on a weekly basis for another 1 year before I could understand the markets sufficiently.
I still have not understood everything as I am yet to master trade automation using robots & EAs.
So speaking from my own experience, you will need to trade actively for about 2 years before you get a hang of forex trading.