According to Wiki, junket is made with milk and rennet, usually with sugar and sometimes other flavourings added. Rennet will curdle milk that is pasteurised and / or homogenised, and it would have been pasteurised milk we used when I was a kid.
The junket I made from Plenty's milk was unpasteurised and unhomogenised, but to get what I would call junket, I did add rennet. I didn't add any sugar, flavourings or colourings, as I liked it just like that. And no culture was used, it was just fresh or slightly aged milk, plus rennet.
I could also make a curd cheese from Hillie's untreated milk (the one from Plenty's milk was not as good). Initially without adding any specific culture, but after a while I isolated the naturally occurring culture and used that to get a repeatable result. But that was more of a lactic cheese than a junket, even though you did get whey coming out when you cut it.