The human brain does not stop developing until around age 25. Parts of the brain that are involved in decision making do not fully develop until that age. However, female brains typically develop around two years earlier than male brains.
The prefrontal cortex, which begins to develop around the onset of puberty, does not complete its development until age 25. This section of the brain controls impulse inhibition, goal planning and organization. The brain's reward system also becomes highly active around the start of puberty, receding to a normal adult level around 25. This overly active reward system causes adults under 25 to seek out uncertain situations to find out whether they might be rewarding.