It took me a couple of days to remember what website the ECHC's nurse quoted, it was from The Australasian Society of Clinical Immunology and Allergy - Home.

More research is needed to determine the optimal time to start complementary solid foods. Based on the currently available evidence, many experts across Europe, Australia and North America recommend introducing complementary solid foods from around 4-6 months. Solid foods should not be introduced before 4 months.
The Australasian Society of Clinical Immunology and Allergy - ASCIA INFANT FEEDING ADVICE
When asked when baby's digestive system is ready for solids, she only said every baby is different. Well that's probably why the experts will continue researching ...