We will never find out.
My father conducted a scientific experiment at 19, to determine his answer to this question. He vaguely remembers passing out.
My control issues are much too deeply embedded for me to recapitulate my father’s empiricism. Once I realise that I am affected by imbibing booze, I get annoyed enough at the impending loss of control that the imbibing ceases. Even if it involves quite yummy cocktails, as my birthday degustation on Monday did.
The limit is I think 5 shots’ worth.
The symptoms only get as far as me being slightly more voluble than usual, and an incipient wooziness. No room spinning or nausea or anything like that.
My threshold has dropped since my twenties too. I was capable back then of downing a Long Island ice tea. Already by 35, I was struggling with half of one.