Pretty much since my early 40s. 1 beer (~5-6% ABV) would be fine if I took care to make sure I was well hydrated and ate something after, but anything above that and I’d be dealing with an all-day headache that wouldn’t respond to pain relievers on top of a night of poor sleep. Sometimes the hangover would start before bedtime. My PCP at the time (since retired) did a blood draw, and nothing popped up as unusual. FWIW, my hangover symptoms line up pretty well with migraine symptoms, but I never received a diagnosis for it. PCP said “maybe it is” and to avoid doing the things that triggered the symptoms and that was that.
I’m sort of between PCPs, the one I’m working with now doesn’t seem to be very responsive, but was in network and I could get in quickly since I was already in the system vs. waiting 6 months.