I've never had "I'm too "old."
I've had plenty of "YOU"RE too old."
But they are both **** tests to see if you've got the goods so I would assume you deal with em the same way.
I say to the young ladies, "actually, YOU are too YOUNG for me, you couldn't handle me." That works REALLY good.
So I would suggest you say something like "yeah, I doubt you'd be able handle me."
JJ