Yes, if they run a comfortable pace that would allow them to talk to a running buddy. That pace is known as LSD (Long Slow Distance). Their bodies are still growing, and they should avoid putting significant stress on their bodies from running. In working up to the 13.1 distance, they should follow the 10% rule and run heavy/light. Here is a reference about the basics of running.
My understanding, after doing 3 of them, is the age limit depends on who is putting on the race and whether or not they must go by the rules of USA Track and Field. The lower age limit might be 14, but I could be wrong. The registration from should clear that up.
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