To clarify (though lots of these points have already been made)...
A baby needs only milk for the first 6 months. Somewhere around 6 months a baby's gut matures and they can cope with more than milk. Not knowing when this is, the guidelines are set at 26 weeks. But never before 17 weeks.
If a child is sitting up reliably, has lost the tongue thrust reflex and can pick up and put food in its mouth, chew and swallow, it is probably displaying the external signs of gut maturation.
The guidelines have been 6 months since 2003. For 20 years before this they were 4-6 months.
Weight is nothing to do with readiness to wean. Big babies don't need weaning any earlier than small babies. Birth weight or weight at any arbitrary age, it's all irrelevant.
Night waking and increased feeds do not indicate a mature gut. They indicate a baby developing.
A breast is not 'sucked dry'. It is a river, not a pond. Your breasts make milk as the baby feeds. If a baby is hungry after a milk feed, putting them back on does give them access to more milk.
6 months is 26 weeks.
4 months is 17 weeks.
Iron stores in bf babies begin to deplete at 6 months but milk doesn't suddenly become iron free and the research is a good indicator to introduced a varied diet, not any indication that exclusive feeding for 6 months should no longer be recommended.
The guidelines have not changed recently, nor are they planning on changing them any time soon.
Instinct does not give you a window into a child's gut. You can no they're hungry, no more, no less.
I do so wish women could be given good, valid information and the myths just left well alone. It's so easy to lose confidence in what you're doing when people are convinced of facts that just don't exist. Making a choice about your own baby is fine, as long as it's informed.