How to have a custom field updated based on current time/date every time I look at the record?

How to have a custom field updated based on current time/date every time I look at the record?

We populate our Lead Records from a form filled out by potential clients.  One of the fields is Birthday and I created a Custom Field in zoho crm to be Age and I made it calculated off Birthday using the formula Datecomp(Now(),${Leads.Birthday})/1440/365

It works beautifully but only when the lead is created.  The only way that field appears to be updated is if I update the Birthday field.  

How can I make it so every time I look at the record, it calculates the Age based on the current datetime?

I believe I have the "Old Professional" version of crm

Thanks,
Marci