This is very easy to find out just go to the following address and replace the Highleted part with your Twitter Username.
http://twitter.com/users/show/
jtperman.xml
Once on the site search for "created_at" (can search by useing Ctrl+F)
The age of your Twitter account is the first <created_at></created_at> tag
If you see my account it was created
Wed June 3rd, 2009 at 12:34:03am
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