Sometime around Bilbo’s fiftieth birthday.
Gandalf: “Hey, can you save me and a dozen idiot dwarves and a hobbit from wolves and orcs?”
Gwaihir: “Sure.”

A few months later.
Gandalf: “Hey, can you save a dozen idiot dwarves and a hobbit from wolves and orcs despite the fact that the morons wouldn’t be in this situation if they’d just split off some treasure for some folks who frankly earned it by slaying the dragon they stirred up?”
Gwaihir: “Sure.”

About eighty years later
Gandalf: “Hey, can you save me from the tower of an evil wizard powerful enough to lock me up in it?”
Gwaihir: “No problem.”
Gandalf: “Hey, while we’re on the subject, can you save the entire continent from literally the most evil being on the planet? The only thing he has that can fly are on horses hundreds of leagues west of here. You just have to drop us off at the big mountain.”
Gwaihir: “Fuck, dude, we’re not your taxi service.”
Gandalf: “Okay. If I call you in about a year, can you pick up a couple of hobbits for me out of Mordor?”
Gwaihir: “Sure.”