I can say from personal experience that age has very little to do with it. At 14, your brother is old enough where its all about tolerance. I've seen 14 year olds who can smoke a ton of pot and not get sick. As for stopping the coughing and puking, I'd say go buy a gram or two of schwag and let him smoke it. By then, he should be ready for at least a hit or two of chronic :rasta: