"A sentence is unduly lenient, we would hold, where it falls outside the range of sentences which the judge, applying his mind to all the relevant factors, could reasonably consider appropriate."
"Reaching the age of 18 has many legal consequences, but it does not present a cliff edge for the purposes of sentencing. So much has long been clear. [...] Full maturity and all the attributes of adulthood are not magically conferred on young people on their 18th birthdays. Experience of life reflected in scientific research [...] is that young people continue to mature, albeit at different rates, for some time beyond their 18th birthdays. The youth and maturity of an offender will be factors that inform any sentencing decision, even if an offender has passed his or her 18th birthday."