Cat Age - How Can You Tell?

I've grown up with cats, and not once can I tell how old a cat is by looking at them. In dogs, it's common to tell because their face begins to have whiter fur specks and their eyes are always droopier. But with cats... I can't ever tell. Do they have the same white specks? Do they just sleep a lot more than usual? What makes them older?

So how can you tell the age of the cat by just looking at them? What makes them look older?