This also should work..

declare @people as table (

person varchar(20),

dob date

)

declare @SDate date

set @SDate= '5/3/2013'

insert into @people(person,dob)

values ('Frank','3/20/1990'),

('Joey','12/31/2000'),

('Sue','2/6/2012'),

('Mary','4/1/2013'),

('Bil','5/3/2012'),

('Bob','1/1/2013'),

('Will','10/1/2012')

SELECT person,

dob,

case when DATEDIFF(MONTH,dob,@SDate)/12>0 then convert(varchar,DATEDIFF(YEAR,dob,@SDate))+ ' Years' else convert(varchar,DATEDIFF(MONTH,dob,@SDate)) + ' Months' end as age

FROM @people

where DATEDIFF(MONTH,dob,@SDate)>=4 and DATEDIFF(YEAR,dob,@SDate)<=12