Don't confuse being the creative director of an agency with being the creative engine of an agency. Sometimes, they're one and the same. But not always.
I've worked at agencies where the creative director, however well-respected, was not the creative engine. Those who came up with the best work, the killer lines and fresh layouts were not always the ECD, the CCO, or even the CD. They were the people who loved their jobs and worked like crazy to make sure their ideas were as good as they could be. They never settled.
It may take you a few years to be a creative director. But you can be an agency's creative engine whenever you decide to be.