To the best of my knowledge, mango is perfectly safe (especially if it's ripe.) But to be sure, you should probably run this question by your pediatrician.
(Personally, I believe that babies should only begin eating solids at the age of 6 months. In my opinion, starting them on food any sooner just adds to the risk of food allergies.)
It is possible that he's experiencing a mild allergic reaction to mango. Does he vomit no matter what quantity of it he eats? If so, I'd hold off giving him any more for a few more months.
Is mango the only food which affects him in this way? Or do other tropical fruits have the same effect?
Again, your son's pediatrician may be the best person to ask - but I suggest holding off.
AOL Health