Reporting on Constituent Age through Analytics.

Hello Brains Trust,

We store the date of birth of constituents through an attribute. We've been able to use one of our Custom Date categories under the Constituent dimension to bring this into analytics.

I'm trying to come up with a formula to convert the date of birth into an age, with our eventual goal being able to display an average age by season / production season / price type category etc. 

I've had some success with the below formula, and the results are correct except that they are showing all the resulting ages as a minus. Any ideas where I might be going wrong?

max(YDiff([Years in Custom Date 02], now([Years in Custom Date 02])))

Thanks,

JH.