I used to be exactly like this. In high school I could stand up and do presentations fluently, It would give me a panic attack but I got it done none the less. Only a few people when I was young knew I stuttered. I was always nervous though but for some wierd reason I could be fluent around people I didn't know well. Once I hit 30 for some reason something switched and now I stutter around everybody and it's horrible. I thought it would get better with age but it's the opposite I guess. That's how I know it's a neurological problem.