firstNameValidator: FieldValidateFn<any, any, any, any, string> = ({
    value,
  }) => {
    if (!value) {
      return 'A first name is required';
    }
    if (value.length < 3) {
      return 'First name must be at least 3 characters';
    }
    return undefined;
  };

         [validators]="{
            onChange: z.string().min(3, 'First name must be at least 3 characters')
          }"

  private initForm(): any {
    return this.fb.group<Person>({
      // personal info
      firstName: [null, Validators.compose([Validators.required, Validators.maxLength(100)])]
....
}

         [validators]="{
            onChange: [z.string().min(3, 'First name must be at least 3 characters'), z.string().max(100, 'First name must less than 100 characters')]
          }"