Determining Age But Have the Cell Show as Blank if No Birthdate

I have a list of people with birthdates, some with no birthdates. I created a column to show what their ages are but the blank cells show a number (in my case, the number is "122". What formula do I use to leave the cell blank if there is no birthdate? I have spent hours on this but nothing works.

The formula I'm using to calculate the ages is as follows:

=(YEAR(NOW())-YEAR(A2))