Question: At what age did Jesus realize who he really was (the Son of God), or did he always know? Thank you
Response: Scripture tells us very little about the early life of Christ, but on this point we do have something to go on, that is, Luke's report of Jesus in the temple (Lk.2:41-50). This passage tells us that He and his parents were accustomed to go to Jerusalem every Passover (according to the commandment), and that, when Jesus was twelve, He stayed behind after the feast. It was on this occasion that He told His parents, "Didn't you know that it was necessary for Me to be about My Father's business?" Therefore we can say with complete confidence that, by the time Christ had attained maturity (according to the standard of Jewish custom - twelve years old), He was completely aware that He was the Son of God. The second aspect of your question, "did He always know" is a good one, because it touches upon an important aspect of the life and person of our Lord that is often improperly understood. This issue is covered in the Basics Series part 4A under the life of Christ, but let me say now that, in general, Christians often labor under the misconception that Christ somehow "had it easy" until He began His ministry because of who He was. Although we do not possess the details we should wish to have about His early life (or His life in general before the commencement of His ministry), it is a fact that He had to go through the things that all human beings go through - although He is first and foremost divine. "Making Himself nothing", He took on "the nature of a servant" (Phil.2:7), and lived in the humiliation of unglorified humanity His entire earthly life until finally being crucified in our stead. We know well from the gospels that He had no special protection from the elements, no special invulnerability to hunger and thirst, no way to avoid the endless walking His ministry demanded. He was in many ways and at many times "a Man of sorrows and acquainted with suffering" (Is.53:3), not just (though certainly preeminently) in His death. And throughout His ministry He was under the most intense attack anyone has ever had to face, not only from His contemporaries but also from the devil. It is necessary to apply this pattern (of a hard life) to His prior life as well, and also to His childhood in respect to the question that you ask. Jesus did have an unparalleled anointing of the Holy Spirit (Jn.3:34), but as those of us who as Christians also have this most wonderful gift know (though we inevitably do not respond to this gift with anything like the same perfect consistency Christ exhibited), the anointing, blessed as it is, does not exempt us from pain and trouble in any wise. I believe that in Is.53:2, we have a picture of Christ's spiritual growth: "He grew up before Him [the Father] like a tender shoot, like a root out of dry ground". In other words, Christ had to grow spiritually in the same way we all do (responding to the Word and guidance of God: hearing the Word, believing it, living it and ministering it) - and in very difficult circumstances at that (the "dry ground"). So that the advantages He had were more than offset by the opposition He faced and the incredible difficulty of the mission on which He had been sent (i.e., live the perfect life of growing and following God; serve the perfect ministry; give Himself, His life for us all). We know from Matthew chapter four and Christ's multiple quotations from the book of Deuteronomy (for example) that learning scripture was part and parcel of this continual process of growth. How, exactly, He gained access to the scripture (and don't forget, He was a prophet in His own right: Deut.18:15 with Jn.1:25; Acts 3:22-23), or when He came to the complete cognizance of His divinity cannot be pinned down precisely, but my own guess is that is was very early, for by the normative time of maturity, He was already so well versed in this fact (and theology in general) that He amazed the wisest teachers of His day (Lk.2:46-47). But He got to that point by diligent application of the same principles of spiritual growth with which we all have to do. Certainly He did it better than anyone before or since (to a degree not worthy of comparison), but it is for this reason that He is our ultimate role model in every aspect of the walk we are to walk in this life.
In theological terms, the teaching that explains that Christ in His humanity was subject to all the same challenges that we are (and purposely not helped by His deity, so that God's plan might be properly fulfilled) is called the doctrine of "kenosis". Please see also the following links for much more detail on these matters:
The Life of Christ (in BB 4A)
The Hypostatic Union and Kenosis (in BB 4A)
Aspects of the Life of Christ: Jesus' siblings, the man born blind, et al.
Christology: Some Questions on the Life of Christ.
Yours in our Lord Jesus Christ,