Getting Old is Murder by Rita Lakin

Opening lines:

Hello. Let me introduce myself. I’m Gladdy. Actually, Gladys. I’m a self-proclaimed P.I. That’s right, a private eye. Operating out of Ft. Lauderdale. When did I get into the P.I. biz? As we speak. My credentials? More than thirty years of reading mysteries. Miss Marple and Miss Silver are my heroines.

In case you were expecting someone like what’s-her-name with her "A" is for this, then "B" is for that, you know who I mean--working her way all the way to Z. Well, that’s not me. I’ll be lucky if I make it to the end of this book. After all, I AM seventy-five.