How old is old?

I hate to sound like a newbie at being a mommy to a cat but....how old is old for a cat? I have an 8 year old male that has had really good health since I got him (he was five weeks old when I got him) but recently, its been one medical problem after another with him. Is this a normal age progression?

What type of medical problems? Every animal is differant some age faster then others it can have a lot to do with genetics. Most of my cats have lived to about 15-16 years old. My sister had a cat that was almost 20 when he passed. I had one that just passed in December that we didn't know her true age but we were guessing she was about 12 ears old and she got Intestinal Lymphoma and got old real fast. April did not start looking old until about a month before we realized something was wrong. My Cat Dusty Developed HyperThyroidism a bit on the young side about 8 or 9 years old and he started looking like an older cat but he never acted like one, He Died at 15. Dusty mama never looked or acted her age until she turned 16 and was diagnosed with a melenoma in her eye. Even then she still wanted to play. The Same went for my cat Winnie when she was 15 she had cancer and we let her be because she couldn't be treated and in those last months people were always shocked to find out she was sick because she looked so young and didn't look sick. She was though and i could see differances but in her last pictures she did not look old or sick.
   

8 years old is a mature adult, bordering on middle age.
   
This is about when a lot of medical problems start showing up. Diabetes, cancers, a lot of things surface around this time.
   
As the previous person asked, exactly what kind of health problems?