precocious

This term describes a gap between chronological age and mental or emotional maturity. It often carries a hint of admiration for a child's brilliance, but can shift toward a slightly negative or critical tone if the child is perceived as arrogant or "too grown up" for their age. In social contexts, it suggests a person who mimics adult behavior or speech patterns. While a genius is defined by raw intellect, a precocious person is defined by the timing of their development, often appearing unnervingly sophisticated to those around them.