I suggest you refrain from talking to executives "about agile."
My experiences are just a tiny sample size, but I've found they don't care. And why should they? The Agile Manifesto is about writing code (at least, as an executive understandably sees it).
You need a new language that respects the working environment of an executive. They are highly intelligent, highly stressed individuals that have daily conversations where most "agile conversations" appear completely useless. Truly.
They speak in realms of proxy voting, say on pay, analyst forecasts, and organizational performance. They have whirlwind schedules that balance the needs of board politics, social corporate responsibility, and strategic management workshops. They are exhausted, too. And they all care deeply about their company, so much so, that when we start talking "mindset change" and such, they rightfully tell us to go F ourselves.
The Agile mindset has simple, meaningful elements and @mccallam2 is correct that we might talk about the "why," instead... but that phrase is also something we Agile-folk overuse. It's like a wet blanket we throw over the hard stuff.
Don't say the word (Agile) and, for the love, don't ask executives to "play a game" to illustrate.
Instead, work on creating a new language for Agile that resonates with the executive mindset. Speak to them about organizational behavior with business-heavy overtones, yet also speak to the core of Agile (without saying it).
Start with the work of Dan Greening - the five "Agile Base Patterns". I was fortunate to collaborate with him on this topic, but truly, he deserves 100% of the credit... and it is fantastic stuff.
The below link provides an overview, plus embedded links to deep, thorough discussion on each of the five principles. I believe work of this nature helps us understand how to bring Agile to executives in a considerate, empathetic (and effective) way.