It’s never too late for speech therapy. Just go to a clinic that specializes in stuttering therapy. Not every SLP will have experience in this area as our field is quite broad. They will come up with treatment techniques that is best suited for your need!
It's never late for speech therapy. Stuttering is not a disease but a disorders. Conventional therapies wouldn't work, you need a specific system just for stutterers as the mechanical thoughts are not aligned with the speaking system. It involves many mechanical, technical and emotional factors. Even the fear of speaking, or if you are not able to correct your mistakes during your speech, you would need to face all those situations where you should speak.