This article on Slate makes it clear that the only reason I'm not in the major leagues is because I was born in May instead of August.

Jokes aside, this article actually contains some really interesting findings.
"Since 1950, a baby born in the United States in August has had a 50 percent to 60 percent better chance of making the big leagues than a baby born in July."
The reason for this is that July 31 has been the cutoff for "age" in little league, so kids born in August are the oldest in their leagues. It makes sense, but I'm surprised. I assumed that all future major leaguers would've dominated in little league even if they were a little young for their "age."