Yeah, but it's different for each person, so you should ask your dentist who is familiar with your particular case.
If you already have them, then you already have visited a dentist. The only person who will know is your dentist.
Depends how well you take care of them, I've recently had mine taken off, after about 2ish years, but mine were delayed by a couple of months because I broke 2 brackets, but now that they're off I need to wear a plate for atleast 6 months and I think that the plate is worse than the braces themselves because it's harder to keep it clean!
It might be awhile but it'll be worth it. I got fangs and disfigured teeth, I couldn't be bothered with braces and now...it's actually harder to eat with my set.
I had mine for... oh, 16 months? Mind you, I responded well to it and followed the orthodontist's instructions to the letter.