Where it works is
Connects by -
Field type -
Field Options -
Making the same option in a clean (new) layout can sometimes find the problem
1st_illness_Age must be a Number field, not Text.
Using your calculation, first line is ok, second through sixth lines could be similar to .......
1st_illness_Age => 5 and 1st_illness_Age < 14 ; "5-13 years" ;
and ....... last line 1st_illness_Age => 65 ; "65+ years" )