Old recommendations were to wait to introduce “high allergen” foods for as long as possible to reduce the chance of developing the allergy.. but more recent recommendations are to introduce “high allergen” foods earlier than later to reduce the chance of developing the allergy. It’s now recommended to give small amounts of peanut butter regularly as soon as baby starts solids, and that’s one of the most common severe allergies there is. Pretty sure the ONLY thing infants shouldn’t have is honey (non issue for vegans) because of the botulism risk. Everything else is just when you feel comfortable with it.
I’ve mixed berries with her baby oatmeal for breakfast from 6 months on. I mash the blueberries well though, because she had a hard time with the skin of a smashed blueberry irritating her gag reflex in the beginning. Babies have a further forward gag reflex than we do, so it’s not hard to irritate it.