My nephew is 11mo and I've never once heard him laugh. He's a happy baby and is often smiling but I've never heard him laugh.
I have 3 ds they have all belly - laughed from a few months old from either being tickled, blowing raspberries on them or generally making funny faces or doing something silly.
There's no reaction at all from dn if you tickle him. I see him at least 2-3 times a week .