I just turned 40 in March, so I guess I don't technically count, but it's pretty close.
It was hard in my 20's being single w/o kids, because all my friends were having weddings and babies. And it was hard in my 30's being single w/o kids, because my friends' lives revolved around their kids and when we'd get together the spouse would usually be there and I felt like a third wheel. But over the last year or so, it's gotten easier. The kids are graduating high school and moving on, and the marriages, while still solid, have moved to a level of more independence (meaning they don't spend every waking moment together!). So, my friends' lives are starting to be a lot more like mine, and it's easier to be single w/o kids.
If you're asking those panicked "Am I
ever going to get married and have children?" questions, I can't help, because I chose this lifestyle, and am basically content with it.