lots of marathons refuse entry to kids under certain age limits (16 for lots of them)… keeping it fun is a good gauge… I let my kids run 5Ks till they 'trained'… as they found racing fun but training boring that meant they 'self-regulated' till they got to about 8th grade and started running with the HS team… mainly they liked wearing the shirts to school the next week 😉
The site for everyone who loves running.