Who's the oldest?

[Rimbaud]

With regard to Treebeard:

...the oldest living thing that still walks beneath the sun upon this Middle Earth.

This sentence, when studied, reveal numerous qualifiers. Treebeard also says, "...and the trees are older than I am..." when referring to dark and deep areas of the forest. He is not in contention for the oldest living creature, merely the oldest 'living thing that still walks beneath the sun on this Middle Earth'. This suggests something to me of the ephemeral nature of Bombadil. The essence of his faery, for me, is that he does not truly belong or exist in 'this Middle Earth'.

My point, though, is that there are many older things than Treebeard in Middle Earth but they do not 'walk under the sun'. Bombadil is older but is unique in not truly existing on Middle Earth in quite the same way as anything else. Balrogs and first-born creatures and all sorts of Morgothian monsters are also older than Treebeard, IMHO.