Still in my twenties and I have always stuttered for as long as I can remember. Still commenting though, because what you describe sounds familiar to me. I definitely have kind of a 'base stutter' that is always there, but stuff like talking really fast makes it worse for me. I do tons of small exercises to get me used to slower speaking, like reading little poems out loud suuuper slow before going to bed or talking deliberately slow with my partner or a very close friend.