If the data for average rally length is similar for juniors, it’s not for the same underlying reasons as the pros. The pros have big weapons and power and that is why the points are ending sooner.
For young juniors the errors are happening because of impatience, inconsistency due to mechanical or footwork problems, double faults as you mentioned, etc.
I think the underlying reasons for the rally length is very important in terms of guiding us junior development coaches in the field.
