If I were you, the first thing I would do would be to schedule an appointment with my doctor to rule out any underlying medical issues that you might have.
Assuming that all checks out there, I would ask myself if I was happy and content with my life right now - do I feel that anything is missing? Do I have any close friends that I can talk to if I needed someone to listen? Do I have any hobbies and if not, am I ok with that?
If everything checks out in both areas, then I wouldn't worry. I had a friend that had 4 kids. The two older boys - not in their late twenties - had zero interest in dating or sex. They had hobbies and their jobs and were very content with the lives.
Three years ago, one of the brothers finally met and married someone and they are happy. He is happy he waited. The other son did meet someone this year - he will be turning 30 in December.
Both were happy with how things work out. Don't stress over this - if you are happy and content in your life, then it's ok. If you are not, then you might want to talk to someone you trust about this. Perhaps a counselor could help.