I was under the impression that because society back then was patriarchal, there would be more more importance placed on the paternal lines than the maternal lines.
Polycarp, excellent summary. I learned a lot—a lot more than I ever did in church.
Ok, so anything not identified as unusual would be usual.
I don’t know much about this subject, but the latter part of the gospels relate first hand accounts, while these parts are relating the accounts of others. I would assume what is included would be everything known (or accepted to be true), and the age of Mary and Joseph aren’t known, nor are any of the circumstances that weren’t mentioned. Otherwise, if its not everything known, then these would be the parts considered unimportant for others to know for some reason. In that case, the age of Mary and Joseph weren’t considered important, even had they been known.
So yeah, if anything related was unusual, an explanation would probably be included. But the unusual might just be excluded. That doesn’t move any closer to answering the question, unless you accept a subset of (unknown, omitted, irrelevant) as the answer.
It is interesting to see the ways that every nuance is examined to find a clue though.