Therapy is not belated for any client and rare parents know about speech therapies(there are rare knowledges taught bc stutter is a rare disorder) especially if they are educated at not high levels. You can give it a shot cuz it is the last hope for PWS and 58 is not old as a client for therapy at all!But this sucks that speech therapy will misfire on clients and it is still not a magic solution! So it is possible to receive multiple therapies which will cost you stloads of money so that's why I think if your parents never took you to them, it is never a crime cuz not only rare parents know of it but also even though they gained you therapy, you were liklely still to stutter and we cannot think it as a magic solution that can all the time work on clients.