One trade-off we humans suffer for our intelligence is brains that aren’t as well-developed as they could be when we’re born. Otherwise, our heads would be too big for the birth canal. Therefore, unlike most large mammals, many of which can walk and seek food within days or hours of birth, human infants are helpless. Some parts of our brains take decades to complete their development.
This is especially true of the brain’s frontal lobe, which hosts most of our executive functions: short-term memory, memory storage, paying attention, risk vs. reward behavior, empathy, planning, emotional regulation, and more. The frontal lobe, especially the all-important pre-frontal cortex, takes at least until the age of 25 to mature fully (some studies say 30 for men). Until then, no matter how mature a person may seem otherwise, they’re still ruled by the amygdala: emotion, impulsivity, and an inability to fully comprehend the consequences of their actions. Good judgment is always elusive for young adults until the pre-frontal cortex is online and decisions are made there.
While young people are quite resilient, any chemical or physical damage to their developing brains can preclude full development of the frontal lobe, short-circuiting adult behavior. Even though legally an adult at age 18, their rights are still curtailed. For example, the legal age of purchase and consumption of alcohol, marijuana (in some states), and tobacco is 21. Though it would be horribly unpopular, biologically, it would be best to change the minimum age to 25.