The oldest Bitcoin paid to click site as far as I remember is
https://www.coinbulb.com/I used it back in 2016, but let's see what other people have to say in this.
I don't think it's oldest Bitcoin PTC website. There is
https://btcclicks.com/. According to information on website, they are working since 2013. I can't verify it, but when I joined Bitcoin world back in 2015, they were already worked. Though, I have never used this website.
There was another Bitcoin PTC back then, but I can't recall their name.