“It has long been understood that considerations of age and maturity are usually relevant to the culpability of an offender and the seriousness of the offence. Schedule 21 underlines this principle. Although the passage of an eighteenth or twenty-first birthday represents a significant moment in the life of each individual, it does not necessarily tell us very much about the individual's true level of maturity, insight and understanding. These levels are not postponed until nor suddenly accelerated by an 18th or 21st birthday. Therefore although the normal starting point is governed by the defendant's age, when assessing his culpability, the sentencing judge should reflect on and make allowances, as appropriate upwards or downwards, for the level of the offender's maturity. … Therefore, in relation to offenders aged up to 21 or even 22 years, the determination of the minimum term in accordance with the legislative framework in Sch.21 needs to be approached with an acute sense of how inevitably imprecise the statutory criteria may sometimes be to issues of culpability, and ultimately to "seriousness" as envisaged in s.269 itself. The first stage in the process nevertheless remains the prescribed statutory starting point. This ensures consistency of approach, and appropriate adherence to the relevant legislative provisions. Schedule 21 does not envisage a moveable starting point, upwards or downwards, from the dates fixed by reference to the offender's 18th or 21st birthdays. Nor does it provide a mathematical scale, starting at 12 years' for the eighteen year old offender, moving upwards to 13 years' for the 19 year old, through to 14 years' for the 20 year old, culminating in 15 years' for the 21 year old. The principle is simple. Where the offender's age, as it affects his culpability and the seriousness of the crime justifies it, a substantial, or even a very substantial discount, from the starting point may be appropriate. One way in which the judge may check that the discount is proportionate would be for him to consider it in the context of the overall statutory framework, as if Sch.21 envisaged a flexible starting point for offenders between 18 and 21. This would have the advantage of linking the mitigation which would normally arise from the offender's relative youth with the statutory provisions which apply to an offender a year or two older, or younger, and would contribute to a desirable level of sentencing consistency. Due allowance should then be made for the relevant aggravating and mitigating features to produce the final determination of the minimum term, and thereafter the judge should explain the reasons for the determination in open court.”