How long did it take you to be fluent in a second language?

It took me 5 years to become fluent in Spanish. This was done through newspapers, literature, TV, movies, music, and foreign exchange program. I also knew French which helps a lot.

it depends on the language and on your skills

ideally is to have a teacher and to practice with native speakers

and very important> to read many books

Taking Chinese, it took me about 7ish years actually. I attended class every week and did homework, did practice, the whole business.. workbooks, etc. Chinese is a harder language too.

I can speak Spanish and Korean quite fluently and both took almost a year. I think I need to improve my Korean pronunciation though :)

Depends upon your intention to learn. You can learn easily if you put your mind to it.