Formula to calculate what age will be on specific date

HI!
I am struggling with a formula to calculate what a patient’s age will be at an upcoming appointment. I have a column with date of birth and a column with upcoming appointment. The formula I set as:
{Appointment}-{DOB}
This works for anyone who’s birthday has already taken place, but if they haven’t had a birthday yet this year, it is incorrect.
Your assistance is appreciated!
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