Using If/Then with CONCATENATE

Hello,

I am trying to create a column in a list for a SharePoint site where I am calculating the number of years, months, and days someone has been employed.  Currently I am using the below formula.

=CONCATENATE((ROUNDDOWN(((TODAY()-[Hire Date])/365),1))," yrs")

But now I have run into a snag.  I need to only use the above formula if "rehire Date" is blank.  Otherwise use the "rehire Date" to calculate the years, months, days.

Something like this?

=IF([Rehire Date]="0", =CONCATENATE((ROUNDDOWN(((TODAY()-[Hire Date])/365),1))," yrs"),=CONCATENATE((ROUNDDOWN(((TODAY()-[Rehire Date])/365),1))," yrs")

Any help would be appreciated.

Thanks

Nitin