When I was about 11 years old, I was in fifth grade and I knew some eighth graders. Well, the following year, I was 12 and they were freshmen. I started to hang out with them and I was like the “little sister” (I’m AFAB genderfluid now) of the group.
They got into alcohol from one of the freshmen’s brother and they would offer me some whenever we hung out. Curiosity got the better of me, and sure enough, I was drinking pretty much every time we hung out.
Eventually, my parents found out, I quit the drinking altogether and I never hung out with those people again.
I am quite proud of myself, I haven’t had a drink since I was twelve, actually. But I have heard that drinking alcohol can decrease your performance in things so yeah.
On a whole life of exposure to things that give cognitive decline, apart from that happening naturally with aging (of course with overlap between those two things) the effect is probably not that big, but these last years research has shown that no amount of alcohol is safe for brain health. So you probably lost some cognitive function. But thievish probably not that significant against a whole life. And besides brain plasticity (which is mostly activated by using it) makes it so that this is a sort of unanswerable/unmeasurable question.
In short since it is in the past (don’t know how much) and was only a year, and I’m assuming you didn’t go on a weekly blackout drinking session; don’t stress about it too much, that’s not good for cognitive function ;p