1. As far back as I can remember. I believe I was 2 or 3 when I really started, but iirc it's usually not anything to worry about until 5+, a lot of really young kids have a stutter/stammer initially and then "grow out of it." 2. Constantly, even had another stutterer (trying to be part of the cool kids) ask if I was "st-st-stupid" (this wasn't uncommon at all and was most of the bullies' go to insult) when trying to talk to people/read aloud. 3. Luckily started dating after I had mostly gotten it under control. One of the things that bother me the most is people finishing my word when I start to stammer, but if I told them ahead of time that it bothered me they wouldn't do it...too frequently. 4. Treat him like he's normal, don't "find the word" for him, work with him (speech therapy worked wonders for me, there was a program called "Slow & Easy" that taught me to think ahead and speak more slowly, this worked for me but obviously isn't foolproof, and now most of the time you can't even tell that I have a stutter), and one that would've been helpful for me is to make me understand that bullies exist at a younger age, until people started making fun of me for it, I had no idea bullying was even a thing and because they were making fun of me it was my fault (I'm also a ginger so I was made fun of for that too, this was also something I thought was my fault...how it would've been my fault...no idea, but kids.) Basically just give it a year or two then have him evaluated by a speech language pathologist. Shouldn't be too difficult to find one near your location. They'll put him in a program and help him cope/try to come up with a method that will help him control it to some degree.