This simply a case of reaping the fruit of a bad seed planted long ago.
In the beginning, the cutoff ages for Junior and Senior were 16 and 21, targeted at the ages of getting a driver's licence and full legal maturity. With those ages there were a substantial numbers of J&S entries in The Nats, and a lot of contestants paid an entry fee and did not get a trophy.
In a misguided rules change (motivated by the Contest Board Chairman's (successful) plan to get records in the names of his young sons), the ages were slashed to only 14 and 18.
The immediate result was exactly what could be expected. A narrowing of the windows with a drastic reduction in head count.
Furthermore, as equipment became more complex, expensive, and dangerous, MOST events got totally out of reach for Juniors, with the excpetion of piloting a model built and stated by an adult.
The Senior window was narrowed to only four years. In my estimation many of the events are unsafe for this group, too
The current scenario at The Nats is for 1, 2, or maybe even 3 (wildest hope) Juniors or Seniors to put in a flight with an adult's model, thereby "winning" a sure trophy.
AMA would be correct in ending this farse.
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A good "fix" would be to change Junior to 18 and drop Senior, as in the FAI. This might produce enough headcount to justify awards.
In addition, a limited menu of events that would be affordable, safe, and feasible for the under-18 population.