"Young" Master Gandalf

Hi!! I'm new in this forum and I think this is one of the best forums out there dedicated to the works of Tolkien!

I just have a question.

Why did Treebeard call Gandalf as "Young Master Gandalf"?

We know that the Ents were in Arda since the beginning of the creation and they are the older race there - pls forget thoughts and discussions about Tom Bombadil now - But Gandalf is a Maia who existed even before the creation of Middle-Earth. He was even mentioned in Valaquenta in Sil.

So, Why did Treebeard call him young?