The title "father" is honorific and does not denote age nor biological connection. The comments of Ellicott summarise this situation:
(10) Be unto me a father and a priest.—The title “father” is here
ecclesiastical, like “papa,” “pope,” &c, and this title was given to
spiritual directors, as we find in several other passages in the Bible
(2Kings 2:12; 2Kings 5:13; 2Kings 6:21; Isaiah 22:21, &c.). Micah knew
enough of the law to be aware of the extreme irregularity of his
conduct in making one of his own sons his priest.
The Cambridge commentary observes exactly the same thing:
- father] A title of honour given to a priest Jdg 18:19, a counsellor Genesis 45:8, cf. [Apocr.] Esther 16:11, 1Ma 11:32, a
prophet 2 Kings 2:12; 2 Kings 6:21, a master 2 Kings 5:13, a king 1
Benson is very similar:
Jdg 17:10. Be unto me a father — That is, a priest, a spiritual
father, a teacher or instructer. He pretends reverence and submission
to him; and what is wanting in his wages, he pays him in titles.
Matthew Poole adds some interesting detail:
A father and a priest; for, a father; that is, a priest; a spiritual
father, a teacher or instructor, for such are called fathers: see 2
Kings 6:21 8:9 13:14 Isaiah 22:21. He pretends reverence and
submission to him; and what is wanting in his wages he pays him in
Thus, under the idiom and culture of ancient Israel, there was no problem in calling a young priest both "father": and "son" and Josh 17:10, 11 clearly shows.