The others you are looking at may have started a few days before you. Your Profile says "24 months ago" since that is an average but it will actually change to say "2 years ago" when you reach the actual day.
Mine appeared exactly on the day of the month of my anniversary. It actually appeared in the afternoon. And I think I created my account in the afternoon. So that would imply that it happens precisely at the same minute of the day of your anniversary.
So, long story short, look back and try to find the exact day you started. That will be the day you get the accolade. Or better yet, just wait for it. It'll be there. You'll also get an email from HP indicating the milestone.
Congratulations on your success.