OT: Guitar help!

Hey guys! I'm teaching myself to play the guitar. Well, here's my story. I decided about 4 years ago to learn to play the guitar, and I took lessons for awhile. I am left handed, but I learned to play right handed. I did practice religiously for a little while, but some trouble with strumming. I don't know why, but it seemed awkard strumming with my non-dominate hand! Anyways, I kind of gave up on guitar playing, up until recently. I decided, since I'm a lefty, that I would buy a left handed guitar and learn to play again. I am basically having to learn all over again, as everything seems backwards! However, it does seem like it's alot easier for me strumming the guitar than what it was, so I guess that's a good sign.
Anyways, my question is, if I practice, let's say three times a week, about an hour each time...how long do you think it would take - on average - to become decent at playing? I've always been able to sight read music (to a certain extent at least) so I don't believe I'd have a hard time with the music reading part, but just getting the mechanics down. I really want to try to stick with the guitar this time! I've always been able to pick up playing musical instruments quickly, but I never follow through and master anything. I was the beast sax player in our middle school band, but I gave up the sax! Then, I tried learning the piano, but that got too tedious! So, I am really counting on sticking with the guitar, but don't want to stay in beginner mode forever! I can play "When the Saints Go Marching In" okay!
I know each person has different skill levels, but normally, how fast does it take for someone to learn to play the guitar and to play it well (not professionally, but well?)
Anyways, my question is, if I practice, let's say three times a week, about an hour each time...how long do you think it would take - on average - to become decent at playing? I've always been able to sight read music (to a certain extent at least) so I don't believe I'd have a hard time with the music reading part, but just getting the mechanics down. I really want to try to stick with the guitar this time! I've always been able to pick up playing musical instruments quickly, but I never follow through and master anything. I was the beast sax player in our middle school band, but I gave up the sax! Then, I tried learning the piano, but that got too tedious! So, I am really counting on sticking with the guitar, but don't want to stay in beginner mode forever! I can play "When the Saints Go Marching In" okay!

I know each person has different skill levels, but normally, how fast does it take for someone to learn to play the guitar and to play it well (not professionally, but well?)