How high can i get my armor rating before it stops mattering? I heard that after awhile it stops mattering how high your armor is... Like the damage reduction stops at like 550 armor rating or something.

It's in the 600's, methinks. Tempted to say 650, but don't quote me.

between 500-600 i think you may be able to get it higher but i think it caps out your defence around that point

If you wear four pieces of armor, the cap is at 567 displayed armor rating. That translates into 80% physical damage reduction.

http://www.uesp.net/wiki/Skyrim:Armor_Rating#Armor_Rating