First of all, "old one two" doesn't make much sense as a word or phrase. Therefore, finding antonyms for it would be quite difficult. However, if we take the two individual words separately, we can find antonyms for each.
"Old" is typically used to describe something or someone who has been around for a long time. Antonyms for "old" would be terms such as "new", "modern", "fresh", "young", "novel", "innovative", and "recent".
On the other hand, "two" is a numerical value that can be described as "dual", "double", "coupled", or "paired". Its antonyms would be "single", "solitary", "individual", "unique", and "unmatched".