A standard argument here and elsewhere goes something like this;
A: “I think we can identify early texts in the Pali poetry by metre, the 11 syllable verses are Vedic in character, while the slokas are more Classical”.
B: “This proves nothing, the author of the poem may have simply been employing the poetic technique of “Archaism”, and therefore the poem only looks old, but in fact may not be.”
So far I have seen B nominate a comparison between Tennyson and Dryden, between Ludgate and Chaucer, give the example of Spencer by himself, or simply make the argument without any examples.
As a defender of the “A” stance I have found all of these to be very weak tea so to speak.
Having stumbled across one I wanted to give my opponents a much stronger example that it seems to me has so far (so far as I am aware) not been used.
The Bhagavad Gita in Chapter 11, beginning at verse 15 has a long section of Trishtubhs, that at first glance (I haven’t looked deeply yet) appear to be exactly what the “B” team is looking for, an example in ancient Indian prosody of the conscious use of the Trishtubh metre to sound archaic and “Vedic” but probably composed much later than the Vedic era.
So there you go.
I still don’t find the argument convincing (for other reasons I won’t go into here), but if your looking for a good example of what you are appealing to when you say that maybe that Pali passage just “looks” old, now you have one that is actually from the milieu that is under discussion.
Enjoy!