Figure out if he wants to get to more fluency, then you can help him figure out how. I think some stutterers especially later on in life have come to just accept and live with their stuttering and not looking for change. There is no pill to stop stuttering. Many people selling snake oil and many scammers selling a cure. Oh, some stutterers don't want to take about their stuttering also, do don't force it. For some, just supporting them is enough. How to support them? Give them the space and time to talk. Some stutterers like help finishing sentences, some don't. Anyhow, just provide support anyway they want. I am a mild stutterer in my 40s and married with two kids, one that stutters.