As far as I can see if you select something from a combo box, then you would generate corresponding condition into your SQL statement.
For example if your initial SQL looks like
FROM MyTable mt
Now when something from the age combo is selected you would add corresponding condition
AND Age = @SelectedAge
In your code you would also add definition for the parameter as described in SqlParameter Class (System.Data.SqlClient) | Microsoft Docs
So in brief you dynamically add conditions and their parameters when user select something from the comboboxes.
One thing to notice is that SQL Server 2008 is no longer supported so you should use a newer version. See End support SQL Server 2008 R2 (KB 4456242) - SQL Server | Microsoft Docs