The father sets the date (Gal. 4:2)

“They remain

Under guardians

And trustees

Until the date

Set by the father.”

ἀλλὰ ὑπὸ ἐπιτρόπους ἐστὶν καὶ οἰκονόμους ἄχρι τῆς προθεσμίας τοῦ πατρός.

Paul said, “They remain under guardians (ἀλλὰ ὑπὸ ἐπιτρόπους ἐστὶν) and trustees (καὶ οἰκονόμους) until the date set (ἄχρι τῆς προθεσμίας) by their father (τοῦ πατρός).”  Only this letter to the Galatians used this word προθεσμίας, that means appointed beforehand or previously-appointed time.  Paul explained that the young immature heir was under guardians and trustees who said how and what he could do.  This would continue until he reached a certain age that his father had already set up.  Paul was going to compare the Jews under the law to immature heirs to the kingdom of heaven.  The law was like a guardian until Jesus came along.  Do you know anyone who had a trustee or guardian?