Calculate age for all records in one entity

Hi All,

I have one requiremnt. Can you please post any suggessions.

Need to calculate age for each contacts.(It should be dynamically. User dont want to trigger it manually) contact is  having dob field. So age field should be update on every year automatically for all contacts. We are using online crm. So we can't schedule exe. 

So we have written one workflow to update the age field, it will run on every day but this recurring workflow is failing after 7days.

Please let us know if you have any other ideas.

Thanks,

Sravan.J