well they were never human to begin with. They were either created from non human creatures or a spell, i doubt they just showed up out of nowhere.

Well, I never read the novels, but from what I've heard, The Old Ones from the novels are like Originals from the tv series, which are the first vampires.  The difference between the two groups are the Mikaelson family, also known as the Originals were humans once, and they were changed into vampires by magic.  In the novels, the Old Ones were never human to begin with, they were always vampires, but their origin is unclear.

I don't think there are any Old Ones in the show, there are only the Originals and Silas, both of whom were humans before becoming vampires (directly via magic, as opposed via blood or perhaps a bite from other fictions).

I haven't read the novels but the idea that the origin of how the Old Ones truly come from is unknown makes it interesting, I like mysteries.

Two theories regarding the Old Ones: Either they were born as vampires via evolution, possibly indirectly affected by magic or maybe they were created via magic, they were never born the conventional way.

well old ones is merely a sense of perspective, like a 1 year old vampire could be classified as an old one, it doesnt always mean a hundred year or thousand year old vampire. Like they either came out of nowhere, u know, or were born from a species of creatures who had never become human

The Old ones have nothing to do with the show. Aside from Davina using the term in the originals once or twice. The Old ones that  you're thinking of are from the books ONLY.  The show changed the original concept of the Old ones for the screen adaptation. The Old ones in the books were implied to be "born" vampires and most certainly were never human. Klaus is the only actual book Old one to appear in the show. And they changed him A LOT. book Klaus was not hybrid. He was a pureblood vampire that was 100% more insane than Show Klaus. Book Klaus makes show Klaus look like a puppy. So basically The Mikaelsons are the show's version of the book Old ones but completely different. It's very loosely based.

DarkRobin is right. In the books, the orignals are referred to as 'the old ones.' But they were human at first, they're mother tuned them into vampires for protection. 

On the show that's true - there is an Original Family but that's not how it is in the novels. The Old Ones were never human and are over 6000 years old (their origins are unknown).