Version 1.0 came out in February of 2011. However, there were 7 Public Betas before that. The first one came out on October 4, 2010 [1]. By the time version 1.0 was released, Sparrow already had hundreds of thousands of users [2].

(Granted, October of 2010 still isn't ‘a few years’ a go.)

[1] http://blog.sparrowmailapp.com/post/1262858384/40-000-sparro...

[2] http://blog.sparrowmailapp.com/post/2497742134/150000dwnlds