Well firstly it's going to be tricky to answer this question without also exploring what 'PC culture' involves, given that its such a nebulous and loaded term.

However, if we're taking it to mean 'modify language to fit the political climate of the day' I suspect the answer is always, to some degree, but let me tell you as an example about the period I know most well, 17th century Britain.

The political circumstances of Britain in the 17th century certainly led to certain patterns of discourse which one might categorise as 'political correctness'. Two such issues where we can see this is in royalism and anti-Catholicism.

As you might be aware, the English Civil Wars involved the supporters of King Charles I against his opponents in parliament.

What you might not know however is that his opponents, apart from the hardcore minority which eventually executed him(and even this is subject to debate), were very far from anti-monarchist, particularly in their rhetoric.

Pretty much everyone, including some of those who would ultimately put him to death, professed in the early stages of the wars to be supporters of the King, even when they were actively fighting his armies. It was his evil advisors they were against, or so they claimed.

In 1643 the Scottish regime even published the Solemn League and Covenant, a document which involved swearing to protect the King's person and privileges, even though in practice the document was a treaty with the English opponents of the King to send a Scottish army against him.

This continued after the Restoration of Charles II in 1660, as various opponents of the King continued to couch their opposition in terms that reaffirmed their inherent support both for the individual and his institution. There were those who advocated a republic as well of course, but after 1660 their views were not really accepted in the political mainstream. Given that in many conceptions of rightful authority at the time, the positions of many prominent people in society derived ultimately from the Godly authority of the King, it isn't hard to see why couching criticism in these 'politically correct' terms was attractive.

Similarly, the experience of reformation and memories of the Fawkes/Catesby plot and Mary's persecutions, led 17th century discourse to almost require an 'anti-papist' element.

Much as, for example, seemingly contradictory political agendas within the US Republican party today might be couched in similar 'politically correct' terms of individual freedom or patriotism, disperate religious and political visions were couched as opposites to 'popish tyranny'.

So while I can't answer the question of how long 'political correctness' has been around (though I strongly suspect the answer is 'as long as there has been politics) I hope this is a decent example of how the current state of politics has affected the framing of discourse in the past.

Source wise, I'm on my phone so I can't look up details, but everything I've written about should be covered in, for example, Jaqueline Rose, Godly Kingship in Restoration England, Martin Van Gelderen, Republicanism: A Shared European Heritage, and Michael Finlayson, Historians, Puritanism and the English Revolution.