Why would were be used instead of was in that sentence?
"If I
were X, then I would Y" implies that the proposition in X is not true, but the truth of X would cause something else to happen (Y).
"If I were 18, then I would register to vote."
"If I
was" is used in constructs like
"If I was offensive, it was because of lack of education and not out of malicious bigotry."
"If I was unclear, then I apologize."
In this case the proposition X in "If I was X" is not clearly true or untrue.