Age Formula requiring IF, IFERROR Formula for programmatic data

[BlueBunny]

Hi, I am volunteering at a non-profit women's half-way house that provides women with shelter after their incarceration, and during their parole. I am provided the age of the clients coming into the program; however, I am only provided with 12/31/1999 as a catch all for clients that have not been assigned a date yet.
Column B=Birthdate
Column N=Probation

I was able to figure out this formula via YouTube videos:
=ROUNDDOWN(YEARFRAC(N2,B2,1),0)
But I need to add a IF and a IFERROR

[Keebellah]

USE ISERROR

Check Excel functions for the correct syntax (something like below, but not tested

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[davsth]

=IFERROR(ROUNDDOWN(YEARFRAC(N2,B2,1),0),0)

A slight typo in the above answer

[Keebellah]

My mistake, that's what you get when you type it in text and not alltogether focused
Thanks for the correction