What is the ruling on having a child after the the father has passed fifty, and is that considered an injustice to the child?

There is nothing in Islamic law to prevent a man from procreating at any age. The default ruling is permissibility unless there is evidence to the contrary. Indeed, Abraham (peace be upon him) fathered children at an advanced age, as stated in the Holy Quran through the words of his wife: "Oh, woe is me! Shall I bear a child while I am an old woman and this, my husband, is an old man? Indeed, this is an amazing thing." A father is not considered unjust to his child by procreating at an older age; rather, he must raise him well and seek Allah Almighty's help in doing so.