Young has served 6 years as an apprentice to Mary. So there is the answer to the question, he has only been involved at NRL level, with assisting Mary.
The other experiences he has mentioned are very short term appointments that were all assiting rather than actually head coach positions.
Contrast Youngs apprenticeships to that of JD, Holbrook, or even Hornby who have all gone outside the Dragons bubble to develop the coaching career. Like the others, Young needs to move out before trying to move in to a head coach job.
I honestly believe that Young would not have been made an assistant and would not currently be the interim coach of the Dragons if not for his father's intervention.
Nepotism