How to calculate age (in years) based on Date of Birth and getDate()

Question

I have a table listing people along with their date of birth (currently a nvarchar(25))

How can I convert that to a date, and then calculate their age in years?

Answer 1

We used something like here, but then taking the average age:

ROUND(avg(CONVERT(int,DATEDIFF(hour,DOB,GETDATE())/8766.0)),0) AS AverageAge

Notice, the ROUND is outside rather than inside. This will allow for the AVG to be more accurate and we ROUND only once. Making it faster too.