Gov's Rules - Counting

I can't remember when Gov first learned to count, but he's obviously been doing it a while now.

Just before Christmas as we were walking the streets of Toronto, Gov decided he would count to 100.

There were stops along the way, like,

Gov: "...twenty-eight, twenty-nine, twenty-ten....hey, what's twenty-ten?"
Me: "...That's thirty."
Gov: "thirty-one, thirty-two...thirty-eight, thirty-nine, thirty-ten....hey, what's thirty-ten?"
Me: "...That's forty."
etc.

And nowadays, he handles twenty-ten just fine.

But there has been a rule that he followed at all times when counting, from the time he started to learn the numbers over ten.


-------------------------------------------
Counting Rule
The numbers 13 and 15 are not to be spoken aloud.
-------------------------------------------

If someone points at them, you can say what they are.

But if you are counting... you shall not mention these numbers.

"... twelve, fourteen, sixteen, ..." is the way you should count aloud.

I fear that this rule may have been retired.  We recently were reading a book and he decided he wanted to count the page numbers.  When we got to page twelve, he said "twelve", we turned the page, he said "fourteen", and then  a pause as he looked at the page number... "oh, ya, uh, thirteen".

I think it wasn't until then that something concrete about the existence of the numbers 13 and 15 formed in his head.