The frontal lobe, specifically the prefrontal cortex, fully develops around the age of 25. This part of the brain is responsible for higher cognitive functions such as planning, impulse control, judgment, and decision-making. While brain size reaches near adult levels by about age 5, the complexity and functional maturity of the frontal lobe continue to develop through adolescence and early adulthood, stabilizing by the mid-20s. This extended development period helps explain behaviors like emotional regulation and risk assessment difficulties often seen in teenagers and young adults. There is some evidence suggesting differences in development timelines between males and females, with females potentially reaching full frontal lobe maturity slightly earlier, around age 20, but the general consensus centers around the mid-20s as the full development age for most people.