Fifty years old - Jesus is supposed to have been at this time about the age of 33. It is remarkable that when he was so young they should have mentioned the number 50, but they probably designed to prevent the possibility of a reply. Had they said 40 they might have apprehended a reply, or could not be so certain that they were correct.
Hast thou seen Abraham? - It is remarkable, also, that they perverted his words. His affirmation was not that he had seen Abraham, but that Abraham had seen his day. The design of Jesus was to show that he was greater than Abraham, John 8:53. To do this, he says that Abraham, great as he was, earnestly desired to see his time, thus acknowledging his inferiority to the Messiah. The Jews perverted this, and affirmed that it was impossible that he and Abraham should have seen each other.