23 years is ABSOLUTELY not too late. It's like asking if it's too late to be treated for diabetes as an adult. You should definitely pursue speech therapy if its within your budget. It personally didnt do much for me, but it did give me insights into my stutter and I'm glad I did it. As another user said, it will depend on your level of involvement in the process, the skill level of the speech therapist, the type of therapy they use.