Let's not gang up on Jos, here. His pattern of logic is typical of one who has grown up in a forsaken country. Going strictly off of his cynicalism, I would venture to say that his beliefs are a mix between Christianity and the "show me the proof" thought process of most agnostics; which isn't hard to see how or why he stumbled upon it.
Jos, at the end of the day, it all comes down to, as you say, faith. To us, the Bible is the word of God. Regardless of who wrote what, the authors of this collection of works were influenced by God, letting him speak through them for us to see. The word of God is law, and his laws are truth; therefore, the Bible is the proof to those who have faith, and to those who understand the meaning, it is unquestionable.
The common argument for your contemporaries is to undermine our solid foundation which is the Bible, for without that, any and all of our statements are false; similar to pulling out the bottom block of a tower. Through the millennia, I am yet to see any "philosopher", as you would have it, succeed in disproving Yahweh's word as truth. For John to have written his work towards the end of his life, 70 years after the death of Christ, is completely possible even if he were the same age as Jesus. People living until 100 years old is well documented throughout history, and going by scripture, 900 years old wouldn't be completely dumbfounding.
As I said, comfortability is the worst tragedy that could possibly befall a Christian. Some would label me a fanatic, but I would rather be spit upon and persecuted by the foolish for the rest of my life than face the wrath of a God who would hold me accountable.