Does this story seem plausible?

My friend said his cousin who is 16 years old, made this iphone app (cost him very little to make), got it approved by the app store, and made over a million dollars in the following 6 months. Does this make sense, that a kid could become a millionaire in 6 months like that, with the whole process of app development?

No they would be famous and if you haven't heard of them then it is likely not true.