I used to ride a scooter when I was little but not anymore
My younger nieces and nephews love them. It is so great for young children when they are learning to balance especially the ones with 3 or 4 wheels.
Yea, I always see kids riding them around in my neighborhood, my son is only two, but I think I may get one for him
It would be great for him especially the lighter aluminum models.
He still is a bit uncoordinated so I would be worried about him falling down though 
Right, that is why safety gear is so important especially knee pads and helmets at that age.
Yea, that would be a good idea, at least until he got better at it
The other thing you could do for safety would be to get a model that had an additional noise feature that way others would know where he is.