I have no idea whether Newton was a Young Earth Creationist. But I have no doubt at all that he was a Creationist — in the sense that he believed that God created the Universe, that God is "the Lord of Life [Who Is eternally] with His Creatures."
That latter characterization indicates that Newton believed that God not only created the Universe, but is constantly, eternally "in contact" with it.
And a further thought that touches on MrB's earlier observation: It was Newton's understanding that the intelligibility of the Universe owes exclusively to the "fact" that it is the product of the will and mind of the eternal God. It could have no order except as the manifestation of the Logos of divine creation. And if it had no such order, then scientific discovery would be impossible.
Like Einstein (who loved Newton), Newton's motivation as a scientist was to discover the laws that God built into the world.
So I think it's pretty clear that Newton would have rejected Darwin's theory, had he ever heard about it. Which, of course, he hadn't.
That's probably true.
But I would think the relevant question would be whether he would have rejected radiometric dating, since that is the subject of the article. I don't think an assumption that because he would reject one means he would have to reject the other is valid.