Board Thread:General Discussion/@comment-81.105.143.117-20180405014345/@comment-2605:A000:132E:8291:B17D:9AD8:B80A:2748-20180406180212

My first achievement has always kept the same date, regardless of reinstalls, at least using the same acct. That should tell you the first day you played. It would be very difficult to play this game for more than a few minutes without getting that first achievement.

So, that is the best way to find your start date. Although, I have heard iPad and iPhone users no longer have access to achievement history, since there was apparently some change in apple games, or something.