I think the issue most people are having with this achievement being "glitched" is that when they switched servers over the course of the game being out it may been resetting your "start date." Then they seemed to have updated the game, because I notice a lot people that were missing the achievement seem to be getting it now.
This is just a thought I had. Now that they have settled in on what seems like consistent servers I hope there will be no more issues.
I just started the game 1 month ago so I hope in 5 months I get the achievement and will celebrate!