Zachariah was old at the time of Gabriel visit to him.
And they had no child, because Elizabeth was barren, and they both were now well advanced in years. (Lukas 1: 7)
And Zachariah said unto the angel, How shall I know this? for I am an old man, and my wife well advanced in years. (Lukas 1: 18)
He was as old as his wife (Luke 1: 7), both of them are in advanced age.
How old were they?
Advanced age, old age, or elderly age begin at 60 years old.1
Hence, Zechariah and his wife’s ages can be estimated and quantified, ranging from 60 to 70 years old. Without artificial insemination technology, they got biological children.
1. Forman DE, Berman AD, McCabe CH, Baim DS, Wei JY, “PTCA in the Elderly: the ‘young-old’ versus the ‘old-old’” at http://www.ncbi.nlm.nih.gov/pubmed/1727842 ; access: January 20, 2015 3:51 UTC/ GMT