When did Gmail first start signing up people by invite only?

Asked by Buttonstc (27605) December 23rd, 2015 from iPhone

For some stupid reason, It’s giving me a hard time getting into my gmail just because I got a new phone.

All if a sudden it doesn’t recognize me so it’s asking all these additional Qs.

I know that I started my first gmail account when it was invite only but I’m horrible at remembering numbers so am not sure of the year.

Please only answer if you are certain. No guesses please.