Another way to pose this thread and one that covers the same idea is "when did the kingdom of God begin?" I am not trying to change the thread by asking this question, I am merely answering it by using a different approach.
John the baptist, Jesus, and his apostles went all over preaching that the kingdom of God was at hand. We can assume that it was not something that was going to take hundreds of years to fulfill. Jesus says there are some that would not die until they see the kingdom come. Either there are men who lived a very long time or the kingdom came in their lifetime.
There is a passage of scripture in 2 Sam. 7 that an inspired apostle uses to confirm the establishment of the kingdom at Pentecost, let me share it with you.
2 Sam. 7:12-13 And when thy days be fulfilled, and thou shalt sleep with thy fathers, I will set up thy seed after thee, which shall proceed out of thy bowels, and I will establish his kingdom. He shall build an house for my name, and I will stablish the throne of his kingdom for ever.
Nathan is speaking to David of whom Jesus is in direct lineage with. He tells David that one of his descendants would establish the kingdom. This was literally fulfilled by Solomon, we can read about that in the Old Testament. The New Testament reveals that it was spiritually fulfilled by Jesus according to Peter in Acts 2:29-31 Men and brethren, let me freely speak unto you of the patriarch David, that he is both dead and buried, and his sepulchre is with us unto this day. Therefore being a prophet, and knowing that God had sworn with an oath to him, that of the fruit of his loins, according to the flesh, he would raise up Christ to sit on his throne; He seeing this before spake of the resurrection of Christ, that his soul was not left in hell, neither his flesh did see corruption.
Either Jesus is sitting at the right hand of God in his kingdom now or Peter told an untruth.
Please consider these thoughts