Gandalf is an Istari, and one of the Maiar (demigods). He does not age, though he assumes the form of an old man.

Gandalf appeared in Middle Earth in the year 1050 of the Third Age, he departed from the Grey Havens in 3019 of the third age - making 1,969 years.

In Tolkien's world, Gandalf wasn't a man but had the appearance of a man, he wasn't born in the normal sense and, although he did die during Lord of the Rings, he was sent back. When, at the end of the book, he departs over the sea from the Grey Havens, it seems to be considered a one way trip, so it is likely he then left Middle- earth forever.

It must be noted, of course, that Gandalf's history cannot be said to truly begin when he arrived in Middle Earth. Since he was apparently a Maia, one of the beings who at the beginning of time assisted Illuvatar and the Valar in the creation of the World, it would be fair to say he goes back a ways.

Gandal is approximate 32045 years old. He's being sent to help Varda with creation of Arda.