Will, you say, "It is an unfair advantage that HS wrestlers have a better practice situation and wrestle kids up to three or four years older than them during the past three months."

Have those kids not paid their dues wrestling kids 3+ years older than them for three months?

You also consider it an advantage for them to have faced older opponents, and yet you don't want the 8th graders to have to wrestle someone one year older than them. If its such an advantage to wrestle older kids, let the 8th graders wrestle older kids too.