I know that when Lily sacrificed herself for Harry, Voldemort could no longer touch him and any attempted Avada Kedavra on Harry by Voldemort would rebound onto himself, until, of course, he took some of Harry's blood and put it into himself.
Now Harry and Voldemort share Lily's sacrifice and protection and also share Voldemort's soul since Harry is a Horcrux. When Voldemort tried to kill Harry in the Forbidden Forest, Harry was kept alive by his own blood which ran through Voldemort's veins. When Harry then challenged him a second time, Voldemort's killing curse rebounded onto him yet again since the Elder Wand won't kill its master.
But Voldemort shouldn't have been able to die since Lily's blood sacrifice lived in him and Harry should never be able to die either... shouldn't they both be immortal? I don't get it, someone help!
the enchantments would be removed the moment Harry either left Privet Drive by choice, never intending to consider it a home again,I believe so long as he was welcome there the protection would continue to his 17th birthday, regardless of his intentions. Otherwise, they would have ceased in PofA when Harry left the Dursleys after inflating Aunt Marge. This seems further enforced by Dumbledore's request in HBP:I ask only this: that you allow Harry to return, once more, to this house, before his seventeenth birthday, which will ensure that the protection continues until that time.– Xantec Aug 22 '12 at 16:55