"Brains don't fully mature until age 25!" is pseudoscience weaponized by feminists to justify bad behavior. It has been refuted by mainstream academics, libtard mainstream media, and it even has a
Wikipedia refutation.
The concept of a "fully mature" brain is also pseudoscience. This is a complex topic so I will attempt to simplify...
Brain "maturation" = neural pathways becoming stabilized, large reduction in passive neuroplasticity (automatic rewiring), pruning of weak/unused pathways, and so on.
Different brain regions "mature" at different ages, with some individual variability (and presumably some variation between races and sexes).
Brainstem/hindbrain = infancy
Sensory & motor cortex = childhood
Limbic system = adolescence
Prefrontal cortex = early to mid 20s
Social cognition network = early 30s
Hippocampus = never.
Conversely, brain regions begin to decline at different ages/rates. The prefrontal cortex, which feminists constantly ramble on about, is the first to decline — a mere half decade after it "matures"! This is why fluid IQ (raw problem-solving ability) peaks during the early 20s.
Brain maturation does not necessarily equate to "more adult" behavior, it means that your brain no longer adapts automatically. If you have a dysfunctional brain when it reaches "maturity," it can be difficult to repair; I'm sure you've met many old farts who behave like little kids.
"Mature brain" pathways become more efficient, whether they are beneficial to the individual or not, and harder (but not impossible) to change. You can maintain
active neuroplasticity via exercise, metabolic health, constant learning, etc., and in this way "repair" a dysfunctional brain, but it requires conscious effort.
Brains continually change throughout our lifetimes, geared toward different tasks at different stages. So, at what point do we define "full maturity"? The brain hardware + fluid IQ peak of early 20s-30s? Crystalized IQ peak of 60s-70s? "Emotional intelligence" peak of mid 40s?
Via
Salon:
Kate Mills, a developmental neuroscientist at the University of Oregon, was equally puzzled. “This is funny to me—I don’t know why 25,” Mills said. “We’re still not there with research to really say the brain is mature at 25, because we still don’t have a good indication of what maturity even looks like.”According to a 2016 Neuron paper by Harvard psychologist Leah Somerville, the structure of these and other brain areas changes at different rates throughout our life span, growing and shrinking; in fact, structural changes in the brain continue far past people’s 20s. “One especially large study showed that for several brain regions, structural growth curves had not plateaued even by the age of 30, the oldest age in their sample,” she wrote. “Other work focused on structural brain measures through adulthood show progressive volumetric changes from ages 15–90 that never ‘level off’ and instead changed constantly throughout the adult phase of life.” 
