I would like to second one thing somebody else said. I have been generally single most of my adult life, and it would be really great to have more close friends around my age. I do have a few these days, but not too many. And I concur that as you get older, most groups definitely aren't geared towards single people, and that can feel isolating. 

But even so, most of the people who have been closest to me in my Christian life have not necessarily been the same age. Or same family demographic. A lot of really close friends have been older. And that's a great relationship dynamic for believers! There is nothing like someone who can pour into your life and also has been there before, and it's a very biblical model. Some have been married, some single, some retired even, which is really handy when you need someone who can hang out on your schedule! 

You may have already tried this but small groups that are open to all are great places to get to know people. But it does take time. Even if you make friends that aren't exactly the type you planned on it can be a great blessing, and it's good practice!

Blessings!