There are such cases. The syndrome is known as HPPD.
https://en.wikipedia.org/wiki/Hallucinogen_persisting_perception_disorder
One particularly sad case I know of (we both posted on another forum) was this guy who got forced to take a ridiculously strong hit of acid by his "friends" when aged 14. It completely scrambled his brain and he had persistent visual and cognitive hallucinations ever since. He ended up addicted to heroin which he took to make the hallucinations go away. Then he got addicted to speed so he could get things done while high on heroin. And then he had a massive paranoid psychotic breakdown and had be be sectioned. I think he's off the drugs and slowly killing himself with booze these days
That is by far the most extreme example I've ever heard of. It was a massive dose and a still-growing brain. While I wouldn't recommend hallucinogens to a teenager, millions of them take them and make it to adulthood with no ill effects.
There is no such thing as a risk-free drug, but assuming you do things sensibly, the chances of a single psylocibin trip permanently affecting your brain are vanishingly small.
I ummed and ahhed about posting this, because now that you know the condition exists, you might worry about it while tripping. But I think it's important to do these things fully informed. Remember that there are hundreds of millions-to-one chances that you live through without a thought. Walk under some scaffolding? Cross the road? Go swimming? Eat seafood? All orders of magnitude more dangerous than eating a handful of shrooms. You'll be fine, and you should make sure all your co-trippers know to remind each other of that.