Is type casting required?. I think it is not required. Even though it is a varchar type, SQL Engine will convert it internally in this scenario. Please correct me, if I wrong.

The below code will work:

CASE

WHEN [Age (Working Days)] < 30

THEN '1 - 29'

WHEN [Age (Working Days)] < 60

THEN '30 - 59'

WHEN [Age (Working Days)] < 90

THEN '60 - 89'

WHEN [Age (Working Days)] < 120

THEN '90 - 119'

ELSE'120 +'