Officially twitter doesn’t show joining date of an account. But it would be important to know when you are doing research on someone’s twitter account.
The need might be curiosity looking his huge follower number or he might be your competitor. But first of all you want to know is since when he is on twitter.
As an active tweepie it would be hard/impossible to go and check hen he tweeted first time. TwBirthday is a web application to find out the same.
The application also displays your godfather which can be the person who brought you on Twitter.
The birth certificate is providing more info like age index that % of twitter users who are younger than you.
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