I'm 23 and you're basically me when I was around 18. I was afraid of attending interviews due to my speech and honestly thought I'd make nothing of my life, I remember leaving my first job interview thinking ill never get a job. To be completely honest I always start interviews off letting them know I may stumble on my words so just bare with me. This usually puts me at ease and stops them from giving me the WTF face when I start messing up when speaking. My advice is try to get a job where you have no choice but to speak. My first job was working on the phones answering phone calls (we both know how difficult this is). There were good days and many days but it all made be grow and accept this is just how I speak but it can be controlled but not completely eradicated. A fews years later I'm due to start the Police in the coming months. I know its easier said than done but you've just got to put yourself in some difficult situations where you have no choice but to overcome them on your own. There's still many words I want to say to express myself whilst in conversations but just have to put on a slight French accent to get through it. The French accent has bailed me out thousands of times over the years 😂. Just try an accent and it may help you with speaking it certainly does for moi. Good luck mate