Notebook LCD畫面最光亮時仍是灰黃色 (沒有"白"色).

是否老化.... it cannot say that..may be.. but the point is.. it may be your LCD color tune not correct.
Some people will buy such as Spider or Huey to tune the display, make sure the display have RIGHT color tone... if you interest, you can go to the shop and see.
When you use for longer, the Color tune will change... if you already use for phtoos editing... you will know that, every photos or video also have the color tempeture, 6500K is standard.. but sometime will change...