I'm totally self-taught, but listened to alot of my favorite music and read everything I could get my hands on for the first 5 yrs of playing guitar. I took me 2 years just to play decently. I've been playing now for over 10 yrs and, at one time, wished that I had taken some instruction from someone in the beginning stages. I learned and practiced, but it was a long road without an instructor or any constructive feedback. But, the internet has been really insightful. Hell, if you look in enough places, the web will actually show you alot about music theory for guitar.

I suspect with a teacher and consistent practice that you'll be playing decently in 6 mths to a yr or sooner depending on your dedication and your guitar teacher.

I always tell anyone interested in learning guitar that it's like learning another language - spelling, grammar, local phrases - it's difficult, time consuming, and takes lots of practice, patience, and a willingness to try and learn on a consistent basis. You've got to be serious and dedicated, otherwise, your playing won't develop. Good luck!