Being 12-13 and being an idiot like most of the people that receive such comments as "you're probably 12 or 13 or something" tend to be are not mutually exclusive, they just have a very large overlapping region when represented by a Venn diagram.
I purposefully didn't capitalize the first letter, add the apostrophe in "you're", and add a period in my quote. I thought people would figure that out, but evidently not. Just saying.
Edit: Oh, and I'm not saying anything about your intelligence. Just defending the grammar in my example.