Hi Shroom, they may be OK at the moment....age may be on their side but no-one can survive (never mind thrive!) that sort of life for years...will take it's toll in the end....it may not be candida, they may have a heart attack or develop a mental illness. I used to live a life like that, perhaps not quite as bad ;) and was fine...until I got ill after vaccines.
People don't become ill on the day they get ill eg my dad didn't become ill on the day he had a heart attack....yet he didn't have any symptoms at all until that day.
Though I understand your point that they don't have candida as such, they may be unwell with other things so they may have things you don't.
Perhaps it depends on what body type you are....both Ayurveda and Chinese medicine both take the view that certain body types are prone to certain illnesses eg kaphas tend to get mucousy type problems.
Also whatever illnesses/deficiencies your parents and grandparents had/have will influence.