You can only get CA when the person you care for gets DLA
The person you care for must already get one of these benefits:
Personal Independence Payment (PIP) daily living component
Disability Living Allowance (DLA) - the middle or highest care rate Attendance Allowance
Constant Attendance Allowance at or above the normal maximum rate with an Industrial Injuries Disablement Benefit, or basic (full day) rate with a War Disablement Pension
Armed Forces Independence Payment (AFIP)
https://www.gov.uk/carers-allowance/eligibility