Modifying item in a list

I have to use a silly fake example because of proprietary work information, but look at this sentence:

"You are responsible for American League players and for National League players who are 27 and under."

(If you're non baseball fan, all players are in either the American League or National League.)

Question is this: can you prove from the grammar of this sentence that you are responsible for an American League player who is over the age of 27? I know the intent of the sentence, that being, someone else is only responsible for National League players older than 27, this person is responsible for the rest. But a coworker contends that the sentence essentially means once ANY player is older than 27, they are no longer responsible for them. There are obviously better ways to construct that sentence if that's the case, but having a better way is not proof that this explicitly does not mean that.

Is it the second use of the word "for"? The lack of a comma or other punctuation before "who are under 27"? Or is my coworker right, the sentence is poorly constructed and can be taken either way?

What grammar rule applies here?