Have you done Agile is a common interview question these days if you're applying for a position related to software development. A few quick thoughts:
When C++ came along many of its features formalized practices that skilled C programmers were using already. For example: encapsulation. Of course C++ introduced many new concepts.
Similarly, Agile (however you define it) formalizes some practices that development groups had been using before the term Agile was coined and added more. For example, timeboxing of releases was a common practice at Dolphin (1984-2005). The concept of a daily build was in use at Microsoft as described in the book ShowStopper (Windows NT development). Zero defect milestones were described by Jim McCarthy in The Dynamics of Software Development. Pair programming was around before XP was coined.
The point is that Agile builds on the past and many of us have done Pre-Agile in various forms and should use this experience to adapt to Agile in whatever form it takes in your development shop.
For more thoughts on Agile check out my posting on the book Agile Project Management with Scrum.