I think this is also interesting. Last week in a Scottish Court a 21 year old was not given a custodial sentence for raping a 13 year old when he was 17 after following Scottish Sentencing Council's Guidelines. The guidelines link to a paper about the cognitive development of adolescents and this is part of the executive summary:
"During adolescence and within normal individual development, an imbalanced growth pattern is observed between the brain regions governing emotion and mood, like the amygdala, and those involved in executive functions (those that provide the cognitive abilities which are necessary for prosocial behaviour, successful goal planning and achievement), like the prefrontal cortex. Converging findings suggest that this latter brain region is the last to reach maturity, leaving adolescents with immature and compromised core cognitive abilities for much of this developmental period. This immaturity, when coupled with the increased motivation to achieve rewards observed to coincide with puberty, is thought to be the most likely underlying mechanism contributing to the poor problem solving, poor information processing, poor decision making and risk-taking behaviours often considered to typify adolescence. Evidence suggests that the influence, or presence, of peers further exacerbates these tendencies."
The Scottish GRR however suggests that a 16 year old has the cognitive development to make a decision about gender reassignment (a lifelong decision according to their proposal).