We seem to take for granted that "c'mon, it's [current year]" can be used as a dismissive remark against anything we see as outdated. Justin Trudeau famously said "because it's 2015" when asked why he'd insisted on having a 50/50 gender ratio in his cabinet; at the coronation of Willem-Alexander of the Netherlands, a (tiny) group of anti-monarchy protesters simply used "it's 2013!" as their slogan; and a common response to ideas seen as overly conservative is "welcome to the 1950s."
However, when you think about it, it's not as self-explanatory as it seems. It implies a view of history as a march of progress towards ever better ideas, a sort of "Whig history" if you will. So, when and where did this kind of rhetoric first appear?
While he doesn't use that phrase exactly, Humfrey Barwick's A breefe discourse is a good example of that attitude dating back to at least the late 1500s. At the time firearms had almost completely replaced longbows in the English army and Barwick was writing in response to traditionalists who opposed the abandonment of what they considered their national weapon. He spends a great deal of time arguing that while the longbow may have been the best weapon on the battlefield in times past warfare had greatly changed due to the introduction of firearms. He gave multiple examples of how what used to be considered sufficient armor in the past was far weaker than the armor being used today.
Sir John Smythe in particular he accused of trying to prove archery's effectiveness with examples which were 200 to 2000 years old at the time.
"And whereas Sir Iohn Smith doth rehearse ma∣nye and sundrye exsamples of victories and ouer∣throwes, giuen by the force and effect of Archers, some aboue 2000. yéeres since, and some 200 yéeres since, and the most betwixt these times: but what hath béene doone since the perfect knowledge of fire weapons hath béen in vse? and wheras Manuell the Emperour of Constantinople, had in his armour or Target the number of 30. arrowes sticking: one Harquebuze or Musket shot would haue dispatched the matter,"
He even sarcastically asks if England should also give up its cannons and go back to using battering rams and other weapons fit for savages.
"what, shall we refuse the Cannon and fall to the Ram againe? or to knowne weapons more meeter for Sauadge people then for puissaunt Princes, that are able to maintaine those of the greatest force?"
Edit: A full text can be found here http://quod.lib.umich.edu/e/eebo/A05277.0001.001?view=toc