When I was a baby in the 70's, my mom fed me rice cereal with formula in my bottle at 2 weeks old, I was on orange/yellow veggies at a month, greens at 2 months and by 6 months if it came in a jar I ate it. When my kids were born I, being decidedly old school, didn't wait until 6 months. All of my kids were given rice cereal in their bottles before they were a month old (and as soon as they got it, they all slept through the night on their full little tummies). By the time my pediatrician gave me the thumbs up to introduce ANY food to my kids, they had been dining for months.
My brother and his wife had kids in the same area, same time frame, same types of baby food and yet his wife followed the doctor's instructions to a t. She didn't introduce a thing until the doctor said she could and both of her kids had colic and they each have a different, severe food allergy now.
That's anecdotal though- the medical evidence is that early weaning leads to increased risk of coeliac etc as the gut is "leaky" for big milk molecules, so allows gluten through to the immune system, plus there's a genetic component so as the population gets bigger, we get more knowledgeable and so have more failure to thrive infants surviving to adulthood and passing on their genes, so there's an increased incidence of these things.
It is, of course, an arbitrary 6 months thing, some infants may have mature guts at 3 months, some at 5, some later, but 6 is chosen as the safe average. And of course if you didn't give gluten and dairy until 6-months- that lessens the risk, even if you've weaned on rice and veggies earlier.
My own anecdotal evidence is DH- like you raised in the 70's - cereal in the bottle at weeks old, weaned very early. He grew up only able to tolerate one food- chicken. Now as an adult he loves his food and his range has greatly widened, but he has the most awful gut reactions to nearly everything, including any stress. He had to give up competing as he couldn't leave the toilet in time for the race!
My own two were raised on modern advice- breastmilk only until just before 6 months. They're both fine, with a varied diet and no gut issues.
Having said that- I am a scientist and very sceptical of non-diagnosed "intolerances". There's a huge difference between a true coeliac eating gluten, and someone who says they are gluten intolerant because they think it bloats them, or constipates them, or whatever.
The whole biscuit thing sounds decidedly odd
I still can't work out graham crackers either, are they like digestives (biscuits
), or crackers, like jacobs cream crackers? Who's Graham?