[Peter Debelak]

Well, YP, it seems to me that the word "eldership" does appear in the New Testament. It isn't a derivation of /prebeturos but rather the greek word /gerousia. Strongs number 1087. Its the word to refer to the Sanhetrin in, for example, in Acts 5:21. Here's some historical background on gerousia (from Britannica:

: The Gerousia was a body of old men of Sparta from noble families who were appointed (because of their virtue) by the Ecclesia (the Spartan Assembly) for life. This council was composed of the two kings plus 28 Spartiates (Spartan citizens) aged at least 60. The Gerousia presented matters to the Ecclesia, gave advice, and tried criminals.

I'd say this Greek practice, in place before the birth of Christ, should not lightly by ignored in our account of the eldership.

Here's some history on the Jewish development of the gerousia:

In Israel before the exile to Babylon, elders functioned as heads of the Hebrew clans (the "twelve tribes of Israel"). The ancient story goes that "seventy elders of Israel" were convened to ratify the covenant which Moses had negotiated with God (Exodus 24). They were portrayed as civil judges whose task it was to settle disputes (Deuteronomy 21 and 22). Later they became rulers with political and military powers (1 Samuel 4.3; 8.4-9).

When the tribal system collapsed after the exile, they retained power as heads of eminent Jewish families. Eventually the families became what we would today call "aristocrats" - such as those with whom Nehemiah had many disputes (Nehemiah 5.7; 7.5). When Palestine came under Greek rule in the centuries just before Jesus, the families were given wide-ranging powers in a council called the Gerousia ("of the elders"), which in turn became the Sanhedrin. This is the "Council of the Elders" referred to in Luke 22.66 and Acts 22.5 (both of which were written by the same person).

Just slowly gathering data... (and doing my darndest not to let my conclusory impulses preceed sound conclusions, if there are any to be had).