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

What about:

DECLARE @DOB datetime
SET @DOB='19851125'   
SELECT Datepart(yy,convert(date,GETDATE())-@DOB)-1900

Wouldn't that avoid all those rounding, truncating and ofsetting issues?