On: Oldest and Fatherless: The Terrible Secret of Tom ...

[valarauko]

Cirdan is certainly the oldest elf in Middle Earth during the period of the LotR. Treebeard and the other ents are probably older.

[fmajid → valarauko]

Gandalf, as a Maia, has got to be older than all left in Middle Earth.

[valarauko → fmajid]

Probably true, though as Gandalf himself refers to Treebeard as old.

In Chapter 5 of The Two Towers, Gandalf calls Treebeard "...the oldest living thing that still walks beneath the Sun upon this Middle-earth." In The Return of the King, Chapter 6, "Many Partings", Celeborn addresses Treebeard as "Eldest."

If Maia are included, then Sauron and Radagast (if still alive) would be just as old.