You have to use age groups - period. There are some 9th graders that are 15 & 16. In a few cases there are some 8th graders that can not wrestle in the 14 & under division. It does happen. They never made 14 year olds wrestle in the 16 & under division back in the day - that was not that long ago. The ultimate decision is up to the parents and the wrestler base on the current rules that have been established. That is the way I see it. 8th grade is the toughest transition for wrestlers - except the transition from high school to college wrestling. It is called attrition.
Every sport starts out with large numbers when the kids are younger. As the level of competition increases the number of participants decreases. FACT
 

at·tri·tion
[uh-trish-uhn] Show IPA

noun
1.
a reduction or decrease in numbers, size, or strength: Our club has had a high rate of attrition because so many members have moved away.

2.
a wearing down or weakening of resistance, especially as a result of continuous pressure or harassment: The enemy surrounded the town and conducted a war of attrition.

3.
a gradual reduction in work force without firing of personnel, as when workers resign or retire and are not replaced.