How To Find Age And Group By Student Number Like (IT%)

I have created a table:

CREATE TABLE [dbo].[Student](
[StudentNumber] [varchar](50) NOT NULL,
[Name] [char](50) NOT NULL,
[Contact] [int] NOT NULL,
[Address] [char](50) NOT NULL,
[DateOfBirth] [datetime] NOT NULL,
[YearEnrolled] [int] NOT NULL,
[Year] [int] NOT NULL;

And insert the following data:

INSERT INTO Student VALUES('IT123456X', 'Ahmad Adam','05-18-1997', '33 Mangis Rod', 19970518, 2013, 1);
INSERT INTO Student VALUES('IT334455U', 'Mary Tan', '01-23-1996', '51 Koon Seng Road', 23-01-1996, 2012, 1);
INSERT INTO Student VALUES('BS123456X', 'Samuel Lee', '03-30-1997', '2 Joo Chiat Lane', 30-03-1997, 2013, 1);
INSERT INTO Student VALUES('BS234234Z', 'Nathaniel Koh', '12-08-1997', '5 Stll Road', 08-12-1997, 2013, 1);
INSERT INTO Student VALUES('BS987987F', 'Siti Faridah', '07-04-1995', '3 Duku Road', 04-07-1995, 2011, 3)

How do i calculate the age and how can i group by the StudentNumber like 'IT%'