It is sooo confusing, I recall reading 1 year, but then came across a place that says 18 months. I googled it and came up with these sites which I thought I'd share here

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http://www.wholesomebabyfood.com/inf...ulismhoney.htm
"...Once an infant reaches the age of 1yr or older, their intestines have a balance of acids that help destroy and fight off any toxins that the botulism bacteria produce...."
"...Even pasteurized honey can contain botulism spores and should be not be given to children under the age of 12 months...."
http://www.askdrsears.com/faq/fit17.asp
"NO HONEY FOR BABIES
"What are the risks of giving a taste of honey to a toddler?"
The American Academy of Pediatrics recommends that raw honey not be given to infants under one year of age because of the rare possibility of being infected with the bacteria that causes botulism (Clostridium botulinum). Once a toddler reaches one year old, their digestive system is mature enough to kill any botulism germs.
Signs and Symptoms:
Symptoms of botulism typically appear between 18 and 36 hours after the infant consumes the bacteria. Constipation is often the first symptom of botulism that parents notice. Other symptoms, which tend to occur in the following order, include:
constipation
flat facial expression
poor feeding (weak sucking)
weak cry
decreased movement
trouble swallowing with excessive drooling
muscle weakness
breathing problems
Infant botulism is a rare illness, affecting only about 100 infants per year in the United States. Most babies will recover fully with proper medical care.
Dr. Jim"
The reasoning behind one year is that usually by age 1 a baby is eating solid food. Once a baby is eating solid foods they are making stomach acid that will make honey safe to consume. The age is arbitrary, what is important is the stomach acid that eliminates and kills any bacteria that MIGHT be present in the honey.