13 months...are you serious?
You shouldn't even be worried about him learning letters until at LEAST 2 y/o.
You can't train babies to read.
My son was reading full books and understanding them right after he turned 3. He has autism, though, and at 5 y/o has a genius IQ (seriously). He is smarter than most adults I know.

We didn't really have to teach him anything that he knows...his brain is like a computer, and it's like he was born knowing how to read and do math. Socializing, though...THAT has been a major struggle. He still won't wave to people or look them in the eye.
My other son is almost 4 and doesn't even know all of his letters yet. And that's fine. Everyone learns at a different pace.
Try not to be a "flashcard mom"...