The braking part of the brain is not finished until the mid to late twenties. A teenager who cannot hold their tongue is not being defiant, they are working with equipment still under construction.

What the research says

Across ages 10 to 23, emotional reactivity declined with age while the ability to regulate emotion by reappraisal improved, and sensitivity to rejection peaked in mid-adolescence. Early practice still counts: in a randomised controlled trial, a twelve-week kindness and mindfulness curriculum improved preschoolers' self-regulation and sharing relative to a control group. Both are ordinary developmental samples rather than young people with serious anger problems.

Strength of evidence: one line of research. A single study, or a theoretical account.