Why is eleven not spelled onety one? Like 22 or 21? i'm a confused onety one year old!

Yeah, or ten-ty-one or something like that :)

I guess our close ancestors wanted the small natural numbers (positive integers) to have their own unique names. 

I've heard a story onece about a child who learned to count, he said:

" ... sixteen, seventeen, eighteen, nineteen, tenteen, eleventeen, twelveteen, thirteen... WHAT ?"

According to Wikipedia.....

In English, it is the smallest positive integer requiring three syllables and the largest prime number with a single-morpheme name. Its etymology originates from a Germanic compound ainlif meaning "one left".^[1]).

You know for many people the teenage years are the most confusing years.

Perhaps that is why those years have the most confusing names ???   Could this be the answer?