Khizath was born in Harad, hailing from a merchant family that has roots in Rhûn. The village they lived in was rather peaceful, and for a few years he lived the life of a relatively normal child. However, few boys of the village would continue to enjoy their childhood, and Khizath would not be among them.
One of the reasons the village was so peaceful is because it made a pact with a powerful warlord. In exchange for protection (from both outside enemies as well as the warlords own soldiers) they would freely give up their sons if he required new men. When such a collection came in his 7th year of life, Khizath was selected among some other boys to join the ranks.

Soon enough Khizath was trained into a warrior - a drone, with his only purpose being fighting at his Lords command. And so he did. It did not take long for the boy to walk the walk and talk the talk, and by his 10th year any thoughts and dreams of childhood bliss were long gone.
While he was considered a lesser soldier by all accounts, he was still taken along for raids and the like, which would continue to mold him into the man- soldier he was expected to become; one that was blindly loyal and would throw his life away if told to do so by his master.

Such loyalty wasn't extended to him, however.

Eventually Khizath was sent into the lands of the Free Peoples under the command of one of the Warlords most trusted captains, [4th age] and under command of the Dark Lord. But this boys story - or at least the one among them - would come to a halt quite fast.
During battle, Khizaths leg was shattered by a rearing steed, and after the battle... he was abandoned. The captain and his men vanished, and the boy - only fourteen years of age - was left to die. He was well and truly alone for the first time in his life, and he had no idea where he was or where to go.

Surviving was hell. He could barely move but he had to find food somehow. I'll spare you the details of all the disgusting things he ate and drank during that time just to stay alive. But that wasn't even the biggest issue. Even if he had food and drink (however horrible quality), he had no medicine. Medicine he needed to prevent dying of infection. Really, he should have died.
A long time he spent lying on the ground, running a fever with pain he felt was killing him, all the while trying to keep his location a secret from his enemies. Parts of his flesh became necrotic due to the bad care and hygiene, and for a while it seemed he may lose the entire leg or even his life.
But... by luck, he did not lose either. He did, however, lose quite some mobility due to the dreadful state his leg was left in. But he was alive, and eventually he forced himself to stand again.
 

Thus his long journey began. He was determined to find his Lord again, to show him he was a survivor and strong, proud as he was to have made it! Yes, he could already see his triumphant return.
Except... Khizath didn't know where he was or where to go. He could not read any maps, nor ask for help.

And so he became lost, wandering with purpose yet without any direction whatsoever.