Aka I'm not quite sure if a comparison can be drawn between jurors and others involved in the CJS. Jurors are a group of twelve, others you have mentioned sit alone or, in the case of magistrates, on a bench of three, so there is a need to free up positions to younger people coming through the system and also to ensure that the mean age does not become too high. The addition of 70 to 75 year old jurors (a number of whom would be excluded by reason of infirmity) would not make very much difference to the mean age of a jury and would ensure that those citizens who in this age group and able to do so, would add the benefit of age and experience to the judicial system.