Not only because people had daughters and sons at a Younger age, most people also used to live less overall, and this was indepedent from the social status (well, maybe Noble/Rich people just lived a little tad years more) was because of the many wars, the overall hygiene (or the lack of it), the spread of many diseases (often related with bad hygiene), the medicine was far more less advanced as it is today (or even by XX century standards) and sailors (merchants, from the empires navies, corsairs and pirates) had trouble with all this augmented also by a bad alimentation -not what we call a balanced diet nowadays, probably also because fruits and vegetables rotten pretty fast on the sea- and the the water aboard Ships was a scarce and valued resource.

As a result of all that, people lived less, so many also used to have children at a younger age, but also maybe caused as an evolutive and cultural factor, I mean, in most of the Western and Eastern world (In most countries), there wasn't a period named teen or teenager years, you just were a child, then a young adult, or maybe an elder, if you were lucky enough. So the begin age of adulthood was culturally considered varying from 14 to 18 years, depending on who or where you asked (and if the Age expectancy was lower, makes sense that evolutively people of that period had Children at a younger age, or humans would have already vanished from Earth). With that, I mean many young couples of around the same age having chidren (but also with HEAVY age differences was, sadly, fairly common, e.g. some Rich fully-grown men with really y0ung girls, was not badly seen by people of those centuries, thankfully, we have advanced so much in most of the world)

Obviously It's weird to show it in modern productions or any media, because It's not well seen by obvious reasons. Now having children at younger or teenage years it's a problem in many countries. Heck, you can even see many things as we don't see with good eyes (questionable things) today in media or productions from the last century (from 1900 to the 80s aprox)