Old person’s teeth?

So I’m bringing my trash cans out a few days ago when one of the little urchins from a house nearby peddles his trike over, looks at me intently and then asks if I have any teeth.  So I open my mouth, point in and allow as how I do. To which he replies something about old people not having teeth. To which I respond that not only do I have teeth, but they are all mine (he’s too young to understand implants!). I then smile at him and give him a full view of my pearly yellowish whites. At which point he nods his head and tell me that he can see them now and I have old people’s teeth.  So now I stand in front of the mirror each morning wondering what about my teeth make them old people’s teeth and how much a cure will cost.