It's not like people 'need' to have been in a relationship by a certain age so no, it's not your fault directly. However, your demeanor being unapproachable or cold may be partially to blame. Very few manage to get into a real relationship without putting in a little extra effort.
No its not your fault. But make sure you are being available and not stand offish. Try initiating contact to a guy sometime. in this day and age that's not a thing to be frowned on at all. Plus it shows confidence :)
Well, I don't know. I got this girl's number just like you and asked her out. over like 2 weeks. Everything seemed perfectly fine. Guess what happened, she canceled the date at the last second on me and never gave a reason. Im taking that since she never been on a date she got scared and canceled, but I don't know. If you have guys ask you out and you do something like I said then it's your fault.
You are responsible for your life. If you're 21 and haven't dated... that's almost definitely some combination of you don't approach or make yourself approachable in places with men, and/or you don't make yourself attractive.
Why do you reject guys? I know I rejected a lot because I never wanted to be in a relationship. Now I gives a guy a chance. But now, I am not happy. They have done so many things. In the passed. Had sex, live with someone. So I am like oh wow.