I don't think it's a matter of complexity as much as it is a matter of development.
Highschoolers have an under-developed prefrontal cortex — this region of the brain fully forms by 25.
> This brain region is involved in a wide range of higher-order cognitive functions, including speech formation (Broca's area), gaze (frontal eye fields), working memory (dorsolateral prefrontal cortex), and risk processing (e.g. ventromedial prefrontal cortex). The basic activity of this brain region is considered to be orchestration of thoughts and actions in accordance with internal goals.[3] Many authors have indicated an integral link between a person's will to live, personality, and the functions of the prefrontal cortex.[4]
> This brain region has been implicated in executive functions, such as planning, decision making, working memory, personality expression, moderating social behavior and controlling certain aspects of speech and language.[5][6][7][8] Executive function relates to abilities to differentiate among conflicting thoughts, determine good and bad, better and best, same and different, future consequences of current activities, working toward a defined goal, prediction of outcomes, expectation based on actions, and social "control" (the ability to suppress urges that, if not suppressed, could lead to socially unacceptable outcomes).
> This brain region is involved in a wide range of higher-order cognitive functions, including speech formation (Broca's area), gaze (frontal eye fields), working memory (dorsolateral prefrontal cortex), and risk processing (e.g. ventromedial prefrontal cortex). The basic activity of this brain region is considered to be orchestration of thoughts and actions in accordance with internal goals.[3] Many authors have indicated an integral link between a person's will to live, personality, and the functions of the prefrontal cortex.[4]
> This brain region has been implicated in executive functions, such as planning, decision making, working memory, personality expression, moderating social behavior and controlling certain aspects of speech and language.[5][6][7][8] Executive function relates to abilities to differentiate among conflicting thoughts, determine good and bad, better and best, same and different, future consequences of current activities, working toward a defined goal, prediction of outcomes, expectation based on actions, and social "control" (the ability to suppress urges that, if not suppressed, could lead to socially unacceptable outcomes).
Source: https://en.wikipedia.org/wiki/Prefrontal_cortex