I noticed that, my account on my site says that I've registered since Apr 2011 lol, I've just launched my website yesterday!
My Website
How to fix this?
It shows as "Registration Date: Yesterday" for me. Where are you seeing it?
I see May 2013 as well. It may be plugin issue, try disabling all plugins in General Configuration (you shouldn't lose any setting) or deactivate them one by one.
you can follow
this method to change that registered date of admin