I've heard claims on both sides of this, that people in all eras found stories of their parents childhoods strange and quaint and had nostalgia for bygone fashion, and conversely that the 1650s and 1690s, or the 1320s and 1360s, or whatever, were so similar to eachother that there was no equivalent notion of the previous decades as we have today.
The present-day tendency to characterize each decade of the twentieth century with a simple stereotype generally dates back to the early 20th century nostalgia for the "Naughty/Gay Nineties", as I discussed in my answer to Dang kids! Or: Why does each generation have such an exaggerated view of fashion in previous ones?
As I discussed in response to Each decade of the 20th century is pretty easily distinguishable from one another in terms of fashion, cultural product, technology, and even social outlook. Were the decades of the 18th and 19th centuries equally as varied and self-contained?, however, the decade is a social construct, and nothing actually changes by that span of time, so it's unsurprising that the phenomenon didn't exist earlier - and the fact that it didn't doesn't mean that earlier decades were actually indistinguishable. Fashion historians like myself can date portraits/illustrations by the clothing and hairstyles in them going back to roughly the "tailoring revolution" of the fourteenth century, when people began to show status with clothing that was cut and constructed in new and fashionable ways, rather than by simply using more expensive fabrics and ornamentation.
I also have an answer to Nowadays, people often wear clothing and styles from past decades. Was this common in the past? (Eg. In the 1920s, were there people wearing 19th century clothing?) which discusses the fact that people didn't really want to wear old-fashioned clothing in everyday life, even as fashion routinely repeated historical forms.
Hello! While we wait for more targeted answers, I've found a few links to somewhat related answers you might be interested in, as previous questioners have asked a lot about how and why artists in previous centuries chose to depict their subjects faithfully or anachronistically. I hope this helps with your middle question.
/u/ARHistChalAl spoke about some of the reasons why Renaissance and medieval European artists depicted Biblical events as if they were in medieval Europe
The ever-prolific /u/[deleted] (though they seem to submit less in recent times) gave a more general overview of the same question, including discussion of the 18th century too.
You may also be interested in a slightly different kind of fashion, in which case /u/WARitter wrote about arms and armour in artwork.
Two other people looked at the same idea as it appears in The Battle of Alexander at Issus — /u/callmesnake13 here and /u/Freevoulous here
/u/GeeJo handles a sort of combination of both of the above topics here, as the questioner wants to know why classical scenes are depicted anachronistically in medieval and Renaissance art.