Because chances are, the author most certainly did.
Case in point: my latest book is set in 1557. And I spent almost as much time researching that time period as I did writing the book!
Here's what one reviewer had to say (amongst other things):
"My problems with this book are, 1 in the 1500s Rose would have been married by the time she was 18 she most likely would have been wed at 14, as a daughter of good family she would've been engaged since birth."
That is simply NOT TRUE. Whilst royal princes and princesses were often betrothed in infancy to secure alliances, the average marrying age of most women in this period was in fact far higher than one might expect - many didn't actually wed until their mid to late twenties.
Furthermore, betrothal agreements between noble families also didn't happen until the individuals involved were of a marrying age. There was an extremely high infant (and child) mortality rate back in those days, it wouldn't have made sense to make wedding plans until it was clear that your son or daughter would actually reach adulthood.
Cases in point: the daughters of Sir Thomas Moore, close friend and advisor of King Henry VIII, as well as both the daughters and nieces of the Boleyns, to name but a few.
Not my usual blog topic but I just had to get this off my chest because it really irks me when thorough research is ignored and even criticised for the sake of a completely uneducated opinion.