Biological fertility as a baseline only slightly modified by social norms seems to be a good guess.
And Juliet was considered way to young to marry (we don’t really know how old exactly Romeo was).
While mid-teens was acceptable age in many cultures to marry and have children by the 17th century that wasn’t really the case. e.g. the average age at first marriage for women was 24 in England in the 1600s
I mean sure, could count as "evidence" but you'd have to be aware of the strength of it.
Imagine in a 100 years time, the next civilisation finds some popular dvd and tries to draw conclusions from it.
Also, I think quite a lot can be reconstructed from even primitive drawings, let alone a whole dvd we know got popular and thus even more relevant for an age.
I do agree with you about getting information from even primitive drawings. I think we differ in our views about the degree and type of information we can get.