Correction: The prefrontal cortex does NOT "mature" early-to-mid 20s: It depends on what you measure. Intracortical myelination — a better biomarker than gray matter thickness, studied in the old "brain matures at 25" study — peaks during the mid-to-late 30s.

The steady myelination decline following the mid-to-late 30s peak results in reduced efficiency: worse problem solving, decision making, memory, processing speed, etc. Brain hardware doesn't revert back to "adolescent" building/learning phase, it just deteriorates slowly.

The "brain matures at 25" claim doesn't even come from the old study, since their sample was age 4 to 21; it was the authors' guesstimate from interviews conducted after the paper was published.

(Debunking myself because I found a paper I saved 3 years ago)