James Montgomery Boice on Paul in Acts 13:
Paul had been in the background for a long time. He seems to have faded from sight, at least to the eyes of the people in Jerusalem. Most had forgotten about him. Paul had spent three obscure years in Arabia, had been perhaps seven years in Asia Minor at Tarsus, and now had spent two more years at Antioch. Twelve years! Paul was getting on into middle age at this point, and he had not been used much—certainly not in any great pioneer work among Gentiles, which God had told him he would do.
But now the call came, and from this point on Paul leads the enterprise to which God had earlier set him apart.
You may be in a time of preparation too, even though you are thirty, forty, fifty, or more years of age. If you are, don’t cut your years for preparation short. If you have been given such years, cherish them and use them wisely. Christians emphasize missions, and missions are important. Don’t give up on missions, but don’t give up on preparation for other Christian work either. The important thing is to keep close accounts with God, study the Bible, learn about others, and serve everyone as widely and as well as you can. It may be that in the years to come, you will look back on this very time and say, “God was working,” and others will note that God was indeed preparing you for even more useful service.