Final answer:
The most rapid brain development occurs during early childhood; however, significant brain changes and cognitive development continue into adolescence and are not fully complete until around 25 years old.
Step-by-step explanation:
The most rapid period of brain development occurs during early childhood. This is a critical period where growth and development are most rapid than any other time after birth, with the exception of infancy which has the fastest growth rate.
During adolescence, while the brain may not increase significantly in size, it does become markedly more complex. This stage of life features crucial developments such as increased myelination and synaptic pruning, leading to more efficient brain function and improved cognitive faculties.
Specifically, the frontal lobes become fully developed by the age of 25 years old. Throughout adolescence and into emerging adulthood, changes continue in the brain that contribute to the individual's cognitive and psychosocial maturity.
Therefore, while the brain grows fastest in early childhood, it also undergoes significant development throughout adolescence and into young adulthood.