I would suggest to seek a SLP ASAP. It gets rough and rougher and he'll get used to of not speaking fluently. I would suggest to not waste time and get him appointments as quick as you could. I had it started when I was 6. My parents being protective af made me believe that people are gonna laugh and don't speak. That all made me awkward nervous and social anxious. I would suggest to never make him feel its a bad thing, however make him to do the speech exercises daily. He's gonna get fluent! ♥️