How does "Know Age" work with bones?

Question

In our campaign we're discovering items from an ancient civilization that nobody knows about, so we're digging around in search for clues about these people.

We already know that they lived up to 600 years (at least some of them).

We also found a mass grave and used the "Know age" prayer on a skull, with a reading of about 2000 years. A discussion followed this discovery because we don't know if this reading is related to the birth of the dead man (that is when the skull was first created) or when the man died (or when the "skull" ceased to be part of a human being and became an "object"). In this case a difference of 600 years matters on how this discovery bound with other information in our hands.

During this discussion we have come across other interesting limit cases: what if I try to know the age of a painting? The result is the age of the paint or the one of the finished work? And when is such work considered finished? What if it is an "incomplete" painting? What if there is paint applied on top of another layer of paint?

Anyway, how we should handle this simple prayer?

TL;DR: Using the first level prayer "Know Age" on a bone, does it read the age of the bone from when the creature was born or when she died?

Answer 1

This is a spell from the Tome of Magic. In general, many spells from the ToM are not very carefully written, but in this case we can use the available information to answer the question. As with many AD&D (1e/2e) questions, this one is also open to interpretation by individual DMs with no official support. (I searched through an online database of 1800 Sage Advice questions from many years worth of Dragon magazines and they yielded nothing on this issue.)

Here are the relevant clues:

Area of Effect: One object or creature

This spell enables the caster to instantly know the age of any single person, creature, or object on which he concentrates.

The Priest Spell Compendium Vol. 2 has the exact same wording as ToM in the spell text, but makes clearer the AoE (Range was given as 0 in ToM):

Area of Effect: Object or creature touched

The priest touches/chooses an object or a creature. Is a bone a creature? No. Is it an object? Yes. (Even entire corpses are not creatures, which is a straightforward statement that has been officially confirmed in other editions of D&D. See for example, this 3e and this 5e questions.)

Now, what is the age of this object? On the one hand this question harkens back to an age-old philosophical paradox known as the Ship of Theseus, but I will leave that aside and argue that the time when the object came to be for all practical purposes what it could be described simply as "just a bone" should be taken as its starting point. From the D&D perspective, the bone would not be described as "just a bone" while inside the body of its living owner, since it was not even an object then. (We know that even objects that are worn by creatures become belongings and get magically harder to target, as they benefit from the saving throws that their owners roll successfully. Moreover, a body of a living creature could then be considered an object as well, which is inconsistent with the distinction between objects and creatures.)

In short, the bone's age is the time passed since it became an object, which happened after the destruction of the owning creature. However, make sure you ask your own DM for the final judgement.