1-4 years = T1
    5-9 years = T2
    10-15 years = T3
    15+ years = T4

10/03/2016 = T1
     01/18/2010 = T2
     01/14/2006 = T3
     12/07/2002 = T4

SELECT
CASE
    WHEN hire_date < DATEADD(YY,-15,GETDATE()) THEN 'T4'
    WHEN hire_date < DATEADD(YY,-10,GETDATE()) THEN 'T3'
    WHEN hire_date < DATEADD(YY,-5,GETDATE()) THEN 'T2'
    ELSE 'T1'
END
FROM your_table