Han Nah, there has been some discussion about lack of concentration, etc., that seems to center around the brain attempting to compensate for its new limitations. Especially if you've been having the usual symptoms, the brain could be fatigued from trying to work around them. I don't know if there are any published studies to back this theory, but it seems plausible to me.
It's good that you're able to work part-time when you feel that you need to, but I wouldn't expect your treatment to be a magic bullet. Whether you choose surgery or radiation, it probably won't make you feel any better (aside from the relief of having taken action), at least not right away. Truth be told, it will probably make you feel worse in the short term. However, what you're shooting for with either procedure is long-term health. Also with either option there is a good chance that you'll be able to return to work and live a normal life.
Yes, there are people on the board as young as you. I was 29 when I had radiation, there are others my age, and I believe that Taylor is 18. Your youth can work for you in recovering from radiation or surgery, so don't knock it. Best of luck!