There is no averege time, depends on the way your teeth are and how long it will take them to fix them. I had braces for a little over 3 years.
If your teeth aren't THAT messed up they're just out of line not croked or anything..?
Some people only need braces for a few months while others need them for a few years.
but it usually really depends on how messed ur teeth are
i have to have mine for the next 2 yrs :'(