who's the oldest?

[Firnantoonion]

It may be possible that he is unaware that Bombadil exists and is older than him

that may be, but he calls himself never the oldest, Gandalf and Galadriel do that.

besides, he does call saruman young, but he does that because he doesnt know exactly what wizards are (he himself says that) and therefore begins to count their years from the day they came into Middle-earth, wich is, with his years, a very short time indeed...