I don't disagree with the discussion with the 350. We have large amount of data on age, injuries, vs. bike sizes. I can't share that data. The line was drawn because of that data. We can talk horsepower, weight, mental side, but these type of rules have to based from data. Sometimes even common sense has to backed with quality data. We simply don't have much data yet on the 350.
Keep in mind.. this rule change is about development and not safety. We want a easier transition from a 85cc/Supermini to a 125cc to a 250F or 350F then eventually a 450F when they are 16. I know this doesn't fix everything.. but you have to stop the bleeding then slowly pull the reins in the direction we need to go.
As for the horsepower argument. The 350 does not produce more horsepower then a 450. But it's not relevant because there's about 30 people in the world that ride a 450F to it's potential. That's why the 350 was created as a option.
Hershey... Here's what's in the rulebook: (Notice the example for clarification)
Section: 1.1; Paragraph: A. 6 (For 2017)
- The minimum age for amateur riders is 12. In motocross events, a rider must be 14 or older to ride a 250cc 4-stroke/2-stroke motorcycle. In motocross events, a rider must be 16 or older to ride a 450cc or above motorcycle. See ATV section 1.4 for ATV age limitations. The age of the rider is determined as of the date of the event, except in youth competition.
Example for clarification: A racer who is 13 years old on the day of the event is not permitted to compete on 250cc model motorcycle. A racer that is 15 years old on the day of the event is not permitted to compete on a 450cc model motorcycle.