Is there any medical condition where a child/teenager has a more higher mental age of maturity/personal development than his actual age would suggest?

No: Children and teen agers can certainly be emotionally and intellectually more developed than they should be for their age, but that's not a medical condition. If, on the other hand, they are physically more developed than they should be, like a six year old who is entering puberty, then that is a medical problem, and it should be addressed quickly.

Gifted?: Having an iq > 2 standard deviations above the mean (>130) is actually not typical development. Iq is a function of genetics + environment. Some gifted kids have social skills difficulties. Taking on adult roles is usually from environmental issues. Read the drama of the gifted child.