I was going to reply that it may be possible not to know you have had anxiety ever since your childhood. But, you may have found or had someone point out to you in an abrupt fashion that you are different to a lot of others.

Thus, you might force yourself to try to do activities that other more confident and outgoing people do but you may find that you are not really having a good time.

This way it is possible to not realize you have anxiety until you are diagnosed.