split and compare date in sql server

ALTER FUNCTION fn_Select_Age_Range
(
@dob datetime
)
RETURNS nvarchar(200)
AS
BEGIN

declare @year int
declare @month int
declare @Days int

declare @AgeRange nvarchar(200)

SELECT 
@year=Years,
@month=Months,@Days=[Days]

FROM

 dbo.fnDateDifference(@dob,GETDATE())
 
 select 

@AgeRange=
SUBSTRING(dmnValue_Text,1,CHARINDEX
('-',dmnValue_Text)-1) +' To '+

SUBSTRING(dmnValue_Text,CHARINDEX
('-',dmnValue_Text)+1,LEN(dmnValue_Text)-1)+' Year'
 
from dmnValue where 

dmnValue_dmnValueGroup_ID=11

and 

@year 

between CAST(SUBSTRING(dmnValue_Text,1,CHARINDEX
('-',dmnValue_Text)-1)as int)

and 

CAST(
SUBSTRING(dmnValue_Text,CHARINDEX
('-',dmnValue_Text)+1,LEN(dmnValue_Text)-1) as int)



return @AgeRange

END
GO