Tinman equivalent of 5:10 mile is around 36:34 10km, but of course this is with the right preparation for a 10km.
So with a 13yo boy, who runs a 5:10 mile on like 15-20mpw, and whom main way to train consist of relatively short intervals repeats (200-600m).
In theory, would you bet he still runs under 40min for 10km ?