It's neurological in the way that your brain is still building new connections, and stuttering evolves along with it. Unfortunately, the brain does not understand that your speech patterns are flawed and how to fix it. What it does know is that certain speaking situations cause you discomfort and fear, so it will "help" you in those by releasing even more stress hormones to make you ready to fight or fight, triggering ticks and all that involuntary tension. It will progressively get worse until you reach a sort of equilibrium where your stuttering matches your anxiety levels. You can see here how naturally more anxious individuals can easily hit rock bottom. If anything, this should be a sign to immediately pause any time hogging hobby that you have right now and train yourself daily on how to manage anxiety and speak in a better way. There are good books and videos on YouTube, each with their own approach but pretty much same fundamentals.