I have an 8 y.o. with the same circumstances you describe OP and he gets 3 showers a week. He does not smell at all (like DH, it's remarkable).
Here's what I wonder, though. Should we be in the HABIT of bathing daily, just to get in that rhythm, because puberty-stink is right around the corner? There will come a time when 3x a week won't cut it, because he'll be creating B.O. daily, and I wonder if he'll balk at daily showers then since he's not used to it.