How old was Zacharias when John the Baptist was born?

The New Testament does not give an age for Zachariah, only that he, according to his own Words "I am an old man" Luke 1:18. Using the Old Testament as our commentary, according to Numbers 8:24-25, the age of service for the Levitical priests was 25 to 50 years of age. With 50 being the mandatory retirement age, he would have been a maximum of 49 at his visitation. If his retirement was within the next 9 months he would have been 50 at John's birth.

His exact age isn't given. Luke 1:7 says that he and his wife Elizabeth "were both well advanced in years."