It’s definitely not too late to get him to a reputable speech therapist. I started going to a good therapist in my mid 30s. I would recommend finding someone who doesn’t do what is called “fluency shaping” and instead find someone who understands avoidance reduction. It’s harder than it seems so it’s worth calling around. I have found that certain therapists can do more harm than good bc they can make you feel like a failure if you continue to stutter even after / during therapy. Good on you for trying to help your brother. He is lucky to have you. Just remember, it’s not too late and it’s not too late for him to find a partner who understands speech issues and will love him just as much as they would love a fluent speaker. Many of us stutterers are in healthy, loving relationships despite the stress of our speech (I am, for example). Also just make sure he knows he can talk to you about it and that you have the time for him no matter what. That can be invaluable. Hope that helps.