From the examples provided DL Campbell is the youngest at 20 years, 24 days.
Of course the youngest recipient could have earned his award in1899 for example. Also, using gazette date provides a common data point for all recipients, but in the case of Hunt and othert gallantry DSOs would you use the date of the action?
That's an interesting point. At what point did they 'earn' the DSO, when an act was performed or when the act was recognised? As it is not clear how many DSOs were earned, the only common comparator is the LG date so I would go with that.