Brain damage from LSD is not possible. The closest thing to this that can occur is HPPD (hallucinogen persisting perception disorder), where basically visual distortions and other effects from the trip persist after the drug has worn off, often accompanied by anxiety and derealisation/depersonalisation. However bare in mind that this occurs only in a small percentile of users, and usually only after repeated overuse of a psychedelic or psychedelics. Any psychedelic can cause this though I hear about it most often from NBOMe and less often 2C-x use, then LSD use, and least often mushroom and tryptamine use. So basically, I wouldn't worry about HPPD, but its good to be aware of it (avoid tripping too regularly on the same substance essentially).
Psychosis, bipolar, schizophrenia, and other mental illnesses like these cannot be caused by psychedelic use. The problem is that they can cause a user who was predisposed and would have otherwise developed these issues with time, to develop these issues more rapidly and dramatically. This can either happen as an extreme psychotic or mental break during an experience itself, or during the aftermath of a difficult experience. However the age of onset for these illnesses in males is early 20s, so at 26 you should be in the clear for this. All psychedelics have the potential to bring these issues out, though I hear about it more from LSD. This could just be because LSD is more popular, or it could be related to the dopamine action of LSD which is quite unique from most psychedelics (dopamine is believed to be involved in psychosis). Also overuse of psychedelics can cause not necessarily mentally ill, but specific types of users, to become a little 'out there' with wacky beliefs and what not after tripping. But IME this dissipates in them when they stop using psychedelics so regularly.
I think you should be fine to take LSD, and I hope what I explained makes you less worried about the common concerns people have that you mentioned. Just make sure to have a good set and setting, the outdoors (nature, not a city) is beautiful on psychedelics and I recommend it highly, but be with someone you trust and who knows you're tripping and is OK with it, or someone who is tripping with you. If you are outdoors make sure it is not a very public or crowded place. If indoors be in a familiar setting like a bedroom surrounded by your favourite possessions. Have your favourite music on hand. Drink plenty of water and try and eat some fruit like bananas or apples during the experience for energy (eating most foods is quite difficult and unappealing while tripping IMO). Be well rested with a clear schedule for a day or two after you take it so you can relax. Otherwise do not worry too much about 'will I have a good trip', 'will I have a bad trip'. There are no bad trips unless you have some kind of mental illness lurking IMO, there is just a scale of more difficult to less difficult experiences. What I'm saying is it's quite likely there will be points that you may feel uncomfortable, but it's normal, it'll pass, and it doesn't mean you're gonna have a 'bad trip'. As far as dosage, I think 150 micrograms is perfect as a starter. It is bang on the middle of the strength scale, you will get hints of lower dose effects and what happens on higher doses too.
Finally be aware that it is common now for people to attempt to pass off 25X-NBOMe blotters as LSD. These are chemicals that have given people fatal overdoses and also potential brain damage, which can't happen from real LSD. Buy a home testing kit and cut a small piece of a tab off to test, single use ones can be found online for a few pounds/dollars or whatever, and multiple use kits for around 30-50 £/$/€. I hope this helps you, good luck with your experience.
Edit: as for what to expect, it's just futile to try and explain what it's like, especially mentally. Visually, expect morphing and distortion of objects, and fractal pattern overlays on surfaces. You don't 'see things' that aren't there like people seem to think. You may have strange body sensations and your way of thinking will be altered. It's hard to explain anything further, the English meaning of 'psychedelic' is 'mind manifestation' and those two words really are the best description you can get. Just try and expect nothing if you can, however you imagine it will be will certainly not be how it turns out to be.
