If you want to apply conditional validation on 'Voter Age' or 'Member Age' then need to add this input greater than or equal to '18'.
{{userFormGroup.controls.admissionAge.errors.greaterThanEqualTo.message}}
Retirement Age should be greater than equal to Admission Age
{{userFormGroup.controls.retiermentAge.errors.greaterThanEqualTo.message}}
If you want to apply conditional validation on 'Member Age' then you need to add 'Admission Age' field greater than or equal to '18'.
Conditional Expression with type 'string'
{{userFormGroup.controls.memberAge.errors.greaterThanEqualTo.message}}
Shows custom message
{{userFormGroup.controls.otherAge.errors.greaterThanEqualTo.message}}