In the Lord of The Rings trilogy, does anyone know how old Gandalf is? I remember reading that Gandalf was much older than he looked. Do the books ever say how old he is ?
Gandalf is Maia (Spirit), created before the Years of the Lamps roughly 9,000+ years before arriving on Middle Earth. In Valinor he was known as Olórin. He was sent to Middle-Earth in human form around the year 1000 in the Third Age. That's more than 2000 years before the setting of The Lord of the Rings, to help the free peoples fight the evil of Sauron.
Gandalf walked Middle Earth for approximately 2,019 years, un-aging and appearing as a grey bearded human of about 60 years old or so. He was around long before Middle earth was created and before the Years of the Lamps. He, Saruman and Sauron are approximately the same age - give or take. It's difficult to pin down his true age because time had little relevance before the Lamps were set in place. 11,000 years old is a minimum figure. He's likely much older.
Like Morgan said, Gandlaf is a Maiar (spirit). That means he doesn't age like normal humans do. He existed before the creation of the world. He come to middle Earth in T.A. 1000 and left at T.A 3021, so you could say that he was 2000 years on Arda.
He also can't die. This is why when he dies fighting the Balrog he comes back to life (to fulfill his mission -- defeating Sauron). When his mission is complete, he won't die. He will continue to exist as an ethereal Maiar.
Age (as we perceive it) doesn't exist for Gandlaf.