My ds5 seems to be working out square roots for himself.

Yesterday morning he woke me up by telling me two not friends(uneven numbers) can become friends (even numbers) if you add them together. Then he went from that to working out multiplying two same numbers together(eg) two by two is four. Then straight away he wondered aloud what would happen if you did it "upside down" and worked out square roots. All in the sspace of about five or ten minutes.

This seems to me to be a bit further on from counting reliably to ten? I plan to approach the teacher with this, but ds is not co operative in testing situations. All this is coming from him independently on his terms. Any ideas what age he might be operating at?