I thought you had posted a trick question.
Based on the ONE Junior race we've had so far the 15-16-17 year olds can do their own race. If you have a Junior race that kids want to actually win I think it should be a 9-14 or something like that. The older Juniors are strong enough for their respective Senior categories. The youngest ones are not.
In the Junior race we had the 15-16-17 year olds went on to do the 4s (field finish but active at front) and the P123s (made the break, lapped the field, etc). The 9-13 year olds were struggling in the 5s and 4s.
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"...during the Lance years, being fit became the No. 1 thing. Totally the only thing. It’s a big part of what we do, but fitness is not the only thing. There’s skills, there’s tactics … there’s all kinds of stuff..." Tim Johnson