Given a company that has a cross-tested MP plan with NRA defined as 55 and a DB plan covering many of the same employees with NRA defined as 65 (which is more representative of the group's actual retirement experience).

Is it appropriate to use a Testing Age of 65 when performing an aggregate DB/DC nondiscrimination test under 1.401(a)(4)-9©?

The definition of Testing Age under 1.401(a)(4)-12 gives me the impression that the age to use is the latest NRA under any of the plans in the testing group (without regard to which plans the participant is actually participating in). However, I wasn't sure if I needed to be concerned with the Consistency Rule of paragraph (iv) of -9©. I would appreciate any thoughts shared or experiences during audit.

It appears to me that if the retirement ages are deemed uniform, then you test using the latest, which would be 65, and if the retirement ages are not deemed uniform, then you still use 65, so I don't see another option.

This would appear to me to be consistent with the consistency requirements you reference, not contrary to.

Just one reading of the regs. I haven't seen such a test.