For the vast majority of stutters, it is a lifelong condition. I also used to think I would outgrow it but as a 17 yr old abt to be 18 my speech has gotten much more fluent but I still stutter mildly. It will probably get less as you get older and your brain develops more but there is a large chance that it will remain. The people who do outgrow their stutters often outgrow it before their teen years. By your age, it's safe to say that it's permanent.