So where is it recorded anywhere in scripture where Jesus commemorated His birth, or where the Apostles or First Century Church ever commemorated it if celebrating His birth is so important?
The ONLY event that Jesus celebrated and admonished His disciples to commemorate each year, was His death. His birth gives us absolutely NO SALVATION from the penalty of sin which is death.
Only His blood sacrifice - His death - is of primary importance for commemorating according to the Gospels and the Letters of the Apostles.
And while you may see no reason not to celebrate His birthday - there is a scripture to keep in mind when one decides to reason things of God for themselves apart from the bible:
There is a way that seems right to a man, But its end is the way of death. - Proverbs 14:12 & Proverbs 16:25
OK, so you think we shouldn't celebrate Christmas because there is nothing in Scripture that mentions the Apostles celebrating it? If that's the case, where in Scriptures do we read of the Apostles commemorating Jesus's Death and Resurrection? Yes, they preach Christ Crucified and Risen, but did they have any celebrations surrounding it? If not, then are our celebrations of Easter also 'extra Scriptural'?
Christmas commemorates the Birth of our Redeemer. The Apostles probably never thought about celebrating Jesus's Birth; they were too intent on distributing His Message to the world. After the Gospel writers included the story of Jesus's birth, those who read it began to consider celebrating it, so that naturally WOULD have been well after His Death, and not included in the Scriptures.