Blessings Jim B.,You can classify the methods of counting years into two groups. There is Gods method, and there is everybody else.
Gods method is very simple, accurate and with very little confusion. Gods method is the most appropriate when you are dealing with "things of God." Man's methods are multiple and sometimes can be confusing. But man's methods come in handy when your teaching or doctrines no longer fit nicely with Gods calendar.
Here is an explanation of Gods method:
Gen 1:14 And God said, Let there be lights in the firmament of the heaven to div! ide the day from the night; and let them be for signs, and for seasons, and for days, and years:
Gen 1:5 And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day.
A day is simply that time from one sunset until the next sunset. A month is the time from the first sighting of a full moon, until the first sighting of the next full moon. A year equals the time it takes the earth to complete one full cycle around our sun.
The simplicity of the definitions is that they apply and remain valid from the first day of creation until judgment day. I realize that in the beginning one year equaled 360 days. And this was probably valid until the flood or up until the time of Peleg (Gen 10:25 And unto Eber were born two sons: the name of one [was] Peleg; for in his days was! the earth divided; ). Now what in the world would ever justify us using the length of a year from the days of Noah, to explain a prophecy from someone like Daniel over 1000 years later? Those justifications are in "man's methods" and are found nowhere within the Scriptures.
Let's use a day as an example to understand Gods pattern. Throughout Genesis 1 we learn that "the evening and the morning were the # day."
Jos 10:13 And the sun stood still, and the moon stayed, until the people had avenged themselves upon their enemies. [Is] not this written in the book of Jasher? So the sun stood still in the midst of heaven, and hasted not to go down about a whole day.
Jos 10:14 And there was no day like that before it or after it, that the LORD hearkened unto the voice of a man: for the LORD fought for Israel.
Here are we have a day that probably lasted 36 to 48 hours, and God considers it as still a single day. It's not a "prophetic day", but simply a unique day that is counted the same as its predecessor and following day. We are not told whether that year was short one day, the same as previous years, or possibly even longer. God doesn't consider it important enough for our calculations.
In like manner we have the sun dial moving backward 10 degrees for king Hezekiah. (Isaiah 38:8). It is still only a day, but "10 degrees" longer. It does not affect our calculations of months or years.
Now there are many prophetic words that establish a specific number of days in future events. Now some of these future events will be very difficult for the "elect." Therefore, our loving Father will maintain his promised number of days, but it appears that there may be less hours in each day.
Mat 24:21 For then shall be great tribulation, such as was not since the beginning of the world to this time, no, nor ever shall be.
Mat 24:22 And except those days should be shortened, there should no flesh be saved: but for the elect's sake those days shall be shortened.
Therefore, Gods divisions of time are precise for his purposes, though may vary in the number of seconds, minutes, hours, days, etc.. God uses the lights in the fermament of the heaven to make his divisions. You see, He can control these according to His purposes. He doesn't have to depend on man or Timex. Even the wisemen were on time without having to worry about time zones.
I really can't help you with regard to your question about the "church age." You'll need to inquire of the "scholar" who contrived the concept. Though many believe that the "church" began at Pentecost, be it 30, 32, or 33 AD. I learned over three decades ago the importance of segregating scripture from the concepts of man, even when conceived with good intentions. I was arguing with a brother about a certain "scripture." He tried to tell me that what I was quoting was not in the Bible. I was so sure of myself, I was even able to state that the scripture was on the right side toward the top of the page. To my chagrin, I discovered that I was quoting a footnote. Yes, it was in my Bible, but it wasn't Scripture.
Shalom, John