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?
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.
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.