Hearing Loss with Age, Why??

So almost everyones grandparents probably have trouble hearing, I know my grandparents do! So I wanted to do some light research kind of asking why. Why almost every single person as they age, their hearing starts to go and usually gradually gets worse. So I came across these two articles one being from medicine net explaining that half the people 85 and older in the US have hearing loss. Whether hearing loss is small such as missing certain sounds or large being profoundly deaf, it is a serious concern. If left untreated, problems can get worse of course.  I learned that age-related hearing loss or presbycusis is the loss of hearing that gradually occurs in most of us as we grow older. It is one of the most common conditions affecting older and elderly adults. Noise-induced hearing loss is caused by long-term exposure to sounds that are either too loud or last too long. This kind of noise exposure can damage the sensory hair cells in your ear that allow you to hear. Once these hair cells are damaged, they do not grow back and your ability to hear is diminished, explaining why we slowly lose our hearing. Most older people have a combination of both age-related hearing loss and noise-induced hearing loss, interesting stuff.

http://www.medicinenet.com/script/main/art.asp?articlekey=20432&page=4

http://www.nidcd.nih.gov/health/hearing/Pages/Age-Related-Hearing-Loss.aspx