Should be really way simpler

SELECT

dob,

[day],

DATEDIFF(yy, 0, [day] - dob) Years,

DATEDIFF(MM, 0, [day] - dob)%12 Months,

DATEDIFF(dd, DATEADD(mm, DATEDIFF(mm, 0, [day] - dob), 0), [day] - dob) days

FROM (

SELECT [day] = CONVERT(datetime, '1992-07-07', 120), dob = CONVERT(datetime, '1927-04-24', 120) UNION ALL -- 65

SELECT [day] = '2000-06-06', dob = '1915-01-31' UNION ALL -- 85

SELECT [day] = '2003-12-15', dob = '1923-06-22' UNION ALL -- 80

SELECT [day] = '2002-03-22', dob = '1917-01-24' UNION ALL -- 85

SELECT [day] = '2008-02-28', dob = '2007-03-01' -- 0

) d

or even more simple:

SELECT

dob,

[day],

YEAR([day] - dob)-1900 Years,

MONTH([day] - dob)-1 Months,

DAY([day] - dob)-1 days

FROM (

SELECT [day] = CONVERT(datetime, '1992-07-07', 120), dob = CONVERT(datetime, '1927-04-24', 120) UNION ALL -- 65

SELECT [day] = '2000-06-06', dob = '1915-01-31' UNION ALL -- 85

SELECT [day] = '2003-12-15', dob = '1923-06-22' UNION ALL -- 80

SELECT [day] = '2002-03-22', dob = '1917-01-24' UNION ALL -- 85

SELECT [day] = '2008-02-28', dob = '2007-03-01' -- 0

) d

([day] - dob) gives you the age in seconds (milliseconds if you wish), and then you simply figure out YEAR, MONTH and DAY of that value.