This achievement requires you to play until 1453 in which case the game ends. Make sure Ironman Mode is on and the end date is set till 1453 - do not play endless.
I would combine this achievement with some of the others like forming the Roman Empire, 10 thrones, highest Dynasty level etc.
If you are looking to rush through as quickly as possible a 1066 start is going to be fastest and starting as the Byzantine Emperor will help as you start with Primogeniture which means all titles go to your first born son so no succession issues.
As of patch 1.03 your men at arms will spawn instantly wherever you move your Rally Point - use this to quickly put down revolts and win wars. Invest in buildings that improve your Archers and Light Cavarly and just use these Men at Arms - eventually all you will need is your MaA and you wont even need Levies to win.
You can pretty much play at speed 4 or 5 dealing with problems as they pop up letting your vassals expand your land. On your death and start as new ruler you will likely get factions building up, if you have had some wars with hostile religions your prison will probably be full of people so execute them for dread and your problems will go away.