If I may add something, i think getting in the gym and working out is a big one. This is great for EVERYONE to do but especially somebody with a stutter who struggles with confidence. I'm 22 currently and when I was 17-18 I was pretty insecure in general with myself. I couldn't change the stutter but I definitely could change how my body looked. What I've found multiple years later after consistent work is that once I got some muscle and I started looking at myself in the mirror and feeling good about what I saw the insecurity went away for the most part and I because much less concerned about what people thought about my stutter with my new found confidence. The gym was also a great place for me because I didn't have to talk to anyone, I can just go in there with my headphone on and be in my own world. I don't know about you guys, but I've got a ton of frustration and emotion when it comes to my past with my speech impediment and the gym was also a great place to redirect that emotion into making myself a little better. Just thought I'd add that!