Merlin is also a good example of a wise and mature infant; there is a legend, how he was literally the Devil's own son, but was baptized just in time. Now, having a son with the Devil, did not go over well with the authorities. And So, his mother was put on trial. Now, even back then, they're were procedures to be observed, and she was allowed an attorney. Cue Merlin, at the ripe and mature age of seven days, pleading before a court, in the language of the learned, and actually managing her acquittal.
End of the off topic but. My apologies, I can't help myself whenever that story is in the slightest relevant.
I really suppose that in universe, there is some kind of standardised testing.
Jeremy was the one I was referring to earlier. Of course, an assembly arm is a versatile piece of equipment, and would need more intelligence and maturity than, say, a toaster. However, an issue toaster might really screw up your mornings.
Personally, I think of Winslow as 13-ish. Can't rationalise it, but it seems to fit, for now.