Are you 40+, single and happy? If so, what's your secret for staying happy?

Note: I am not single, but I was, and intended to stay that way. I could happily be single again.

I think the key to being a happy single at any age is to be happy with yourself. Making a life for yourself that suits you, with or without a significant other is extremely important. The very first step is to know and accept who you are, all by yourself. When you don’t rely on outside influences (people or events) to bring you happiness, you are in the driver’s seat. You find your happiness through trial and error (and therapy, if necessary!), making a full life on the way. Having a romantic relationship should be the icing on the cake, not the cake itself, you know?

I’m happy single or married, after all, it’s a state of mind. Presently, I’m single and old enough to stay that way.

absolutely. I’m strong in me.

Mid 50s here, never married (much to the dismay of my mother) and very happy. It’s what @augustlan said, it’s about being happy with yourself, not thinking you need to rely on someone else to do it for you.

Given the number of married people who are unhappy, it seems like someone should be happy—perhaps single people?

Happiness has never been nor ever will be based on any other individual. Our happiness is our own to make or break. As @BoBo1946 said anyone can be happy either way and anyone can be miserable either way.

Yes, for 17 years. There’s no secret. Be happy with who you are and plant your own damn garden.