Calculated age with no DOB

Calculated age with no DOB

Hi,

I currently use this formula to calculate age using DOB: 
Year(Now())-Year(${Candidates.Dob})-If(Month(Now())*100+Dayofmonth(Now())>=
Month(${Candidates.Dob})*100+Dayofmonth(${Candidates.Dob}),0,1)

However, not all clients have a DOB value available, in which case Zoho displays 2022 for their calculated age. If they don't have a DOB value in their record, I want to keep their calculated age blank. How can I only calculate age if DOB is available? 

Thanks