[Right Wing Professor]

If a human observer was not present in time 4.5 billion years ago, then the proposition that the earth is 4.5 billion years old must be treated as reasonable conjecture

No, it could be treated as a good theory strongly substatiated by evidence.

As for a 969 year-old human observer, I take it by faith that the biblical proposition is true. However I am disinclined to think the Gregorian calendar was in use when these words were first spoken.

Unlikely the difference between the Julian and Gregorian calendars made much difference to Methuselah's age. Unless you mean we had a 50 day year back then. That would be impossible too.

[Fester Chugabrew]

. . . a good theory strongly substatiated by evidence.

I'm sorry. Is there something about the words "reaonable conjecture" that conflicts with the above? If so, I don't see it.

. . . a 50 day year back then. That would be impossible too.

The biblical account does not specify how long a year is. The word was spoken and had a conventional meaning long before Moses wrote it down. I doubt it was 365.25 days.