Most of us know that Jesus was sent to die. But it is far to simple to suggest that the purpose of Christ Jesus was that of being slain. If it were that simple, Mary and Joseph would have had no reason to flee to Egypt. They could simply have offered Jesus to Herod that he might be slain and perhaps spare the lives of other first born sons. It does sound a bit silly on the face of it, but then to a non-Christian, the idea that Jesus was sacrificed for us sounds morbid.
Jesus didn't begin to teach in earnest until he was approximately thirty, which is an age beyond the recklessness of youth. In fact, He would have been at the peak of human mental and physical developement.
One can only assume that he, or God the Father, was waiting until the time was right or that he was ready.