My son stutters off and on, could it be a sign it will last until adulthood?

My son stutters off and on, could it be a sign it will last until adulthood? I have 3 kids, only my youngest stutters. It started as soon as he started talking but comes and goes (but kinda stays but very discretely). When he was younger, we were on waiting lists for treatment but it always got better by the time it was his turn. He’s 6 1/2 and it suddenly seems to have returned intensely. My dad and aunt have stuttered all their lives. I can’t find much about that specific info past the age of 5. Is this genetic? Could it last until adulthood?