You can expose a six month old to honey as well but their complex and adaptive digestion system still isn't going to kill the botulism spores that might be in it.
"I don't know how this bad thing works, better rub it on my gums" is not a good strategy in general.
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Botulism spores do not "train immune systems". Babies don't have strong enough digestive systems until they're at least six months old to kill the spores.