SQL Query to select all under certain age using only date of birth How can I select all that are under 20 and female from a SQL database?

The table has a datetime for the dob and strings for name, surname, and sex. That is the whole table.

I am having trouble calculating the age. I am not even sure this is possible.

I am using SQL Server LocalDB and Visual Studio 2015.
This is totally possible. 

SELECT *
FROM &lt;TableName&gt;
WHERE DOB &gt; DATEADD(yy,-20,GETDATE())
  AND Sex = 'F'