[HerenIstarion]

Wakening of the Ents by Elves - I always figured that as consisting mainly in teaching the former speech - awaking from slumber. Thing which slumbers is alive by definition. When fully awoke and able to hum-burarum-ram-roms and similar, it is allegedly more alive than before, drowsy as it was, but it were not dead matter, it were 'alive and kicking', though dumb and speechless.

Besides, does Cirdan walk per se? He rather sits on his wossname most of the time, on the very brim of ME.

And another besides - it may be mere slip of the tongue on Gandalf's part - he may have not remembered exeptions right on the spot, or maybe he was reluctant to break an impression of antiquity he was working up in his listeners etc. It would have been lecture rather than recollection if it ran as follows:

he is the oldest of the Ents, the oldest living thing, apart from Iarwain, who is [insert appropriate here] and therefore older, and Cirdan, who was born, as you may know, by lake Cuivienen, which is now lost, that still walks beneath the Sun upon this Middle-earth

And the third besides (being a speculation, rather than statement): Cirdan is an elf - therefore his life would last as long as Arda lasts, even if he's killed and goes to Aman. Tom is unknown entity (whatever my personal opinions), but allegedly not bound by such a trifle as death. Ents, on the other hand, are similar to humans in ageing and dying, which may take a long time, but the process is evident - Ents are old, some of them die, and all of them will die out unless the Entwives be found. So, it may be that Gandalf has mental proviso, including that class of creatures (dying with true death), and that's among those is Treebeard the oldest - for obviously, Tom is an exeption and elves are special.

EDIT. Just another 'walking' thought (supporting third 'besides') - Gandalf is incarnate, therefore living being, and by that he may be the older one - but he does not draw himself in, neither Saruman, nor Radagast - i.e. different class of beings does not count. So I proclaim speculation plausible END OF EDIT

cheers