It's a whole host of different issues. As we age, the lens gets yellow, the pupil can't open as far, and the number of light-sensing cones decreases.

https://www.ncbi.nlm.nih.gov/books/NBK218971/

As for yellowing, "At age 60, the amount of light reaching the photoreceptor cells of the retina is only one-third of the amount seen at age 20. "

https://www.2020mag.com/article/color-changes-as-the-eyes-age

...or better...

https://www.lrc.rpi.edu/programs/lightHealth/AARP/healthcare/lightingOlderAdults/agingeye.asp