I was born with it and am 22 now. Through speech therapy and putting myself out there I’ve been able to get really good at prolongations so my stutter is pretty mild. However I still get stuck on blocks in nervous situations so definitely far from being fluent. Seems like it varies very widely on whether or not you’ll grow out of it later in life and that luck plays a part. If I had to give some advice I’d say to not count on becoming fluent, but do your best to improve all aspects of your quality of life (exercise, diet, sleep, stress management) and work on speech techniques you’ve learned that work. And just live life and see what happens 🤷🏽‍♂️