Intimate confessions and spit-your-dentures-out hilarious commentary - this is observational comedy at its best. How to Grow Old is a stupid title, because the answer is obvious: Don't Die.
Provided you don't die, you are growing old. Don't come to this book under any illusions. It isn't going to tell you how to stay alive any longer.
It won't help you understand the aging process from a sociological and anthropological perspective, and I'm not sure how much practical advice you're going to get.
However, if you happen to want to know what a white, heterosexual, middle-aged man thinks of getting old - from the struggle to stay fit, keep hold of your friends or stay relevant, to why I'm better at doing a dump now than at any time in my life - this book could very well be exactly what you have been looking for.
You might even find it a bit funny.