Probably started with the Victorian illustrators, most of the odd conceptions about these beings mainly did.

Elves are frequently mentioned in Anglo-Saxon literature (I don't know about Irish) but they are generally thought of as wicked creatures ... cows and humans, for example, are "elf-shot", meaning they were suffering from inexplicable sudden illnesses.

Tolkien was professor of Anglo Saxon at Oxford, so he will have known this literature intimately. He chose to depict elves differently for his own reasons.

Cheers!
Ian