“and he went into the whole region around the Jordan.” John baptized in the Jordan but he may have baptized people in other streams and such that led to the Jordan. It does seem that he stayed close to the Jordan, however.
The Bible does not tell us how long John had been publicly ministering and baptizing before Jesus was baptized and started his ministry. It seems logical, however, that it would have been at least a number of months. The prophecy in Malachi 4:6 about John was, “He will turn the hearts of the fathers to the children and the hearts of the children to their fathers, so that I will not come and strike the earth with a curse.” The angel alluded to that prophecy when he spoke with John’s father, Zechariah, in the Temple. The angel told Zechariah, “And he will turn many of the sons of Israel to the Lord their God, and he will go before him in the spirit and power of Elijah, to turn the hearts of fathers to their children and turn the disobedient to the good sense of the righteous, to make ready for the Lord a people who are entirely prepared” (Luke 1:16-17). By the time of John and Jesus, the people of Israel were so confused doctrinally that it seems it would have taken some time for John to travel the county and turn the people back to God and get them prepared for the Messiah to come.
John was six months older than Jesus (Luke 1:26), and for a period of time, both John and Jesus were ministering separately and were both baptizing people (John 3:22-23). Then John was thrown in prison and executed.
“baptism as a sign of repentance.” See commentary on Mark 1:4.