The "one year" point is new , and the reference to those in their late teens is also a new indication. I know a MS who has just been appointed who is 18 and basically spends most of his time playing computer games with his JW pals. (And perhaps the elders should have looked at the guys Facebook page before appointing him.) He would never have been appointed even a few years ago - the WTBTS are definitely lowering the bar.
w909/1p.26par.11AreYouQualifiedtoServe? A newly baptized person has not had time to prove that he will faithfully care for assigned duties. He may lack sympathy for the afflicted or needed wisdom to help fellow worshipers and may even look down on others. Before being recommended as a ministerial servant and especially as an elder, therefore, a man should be “tested as to fitness” and should give evidence of good judgment and reliability. No set time is given for this testing, and individuals vary in rate of spiritual growth.
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w721/1p.21par.43AppointedElderstoShepherdtheFlockofGod While no specific age requirement is stipulated, it is obvious that these ministerial servants were to be grown men, old enough to be married and have children. They were not to be novices in the congregation, but persons who had been “tested as to fitness.” Before being appointed as ministerial servants it would be beneficial if they had been dedicated and baptized for at least some time that would allow for their fitness to be tested.