@Willyoujustbequiet
On developing later:
It's complicated. The structural differences in the ADHD brain are there from birth. But there is maturation of the brain over the first approximately 25 years of life, so that largely on scans that basically show gross structure, after around 25 years the brains of non-ADHD subjects and ADHD subjects look pretty similar. Given this and other findings around the change in symptoms over time, it's felt that ADHD is a condition associated with neurodevelopmental maturational delay -kids with ADHD fall behind their peers with the gap widening over time.
The stage at which that gap becomes clinically apparent and significant will vary from ADHD child to ADHD child depending on severity, symptom profile, and the environment they are in. Inattentive kids rather than predominantly hyperactive fall under the radar for a long time, some girls too because of social behaviour which masks, and some ADHD kids are lucky enough to find themselves in heavily scaffolded supportive environment.
Late diagnosis doesn't mean they didn't always have it, it means that because of these factors and more, the gap didn't become wide enough, or the presentation problematic enough to be recognised previously.
On growing out of it:
As above, a lot of the idea that you grow out of it came from gross structural scans showing that ADHD brains caught up after a period of maturational delay. Such scans probably weren't detailed enough, things like computerised batteries of neuropsychological function and functional MRI (scanning while engaged in tasks of focus, attention, decision making etc) show ongoing differences throughout the life span. The other thing is that there is a gradual change in symptoms as people age which can make it seem like people have outgrown it. E.g. the hyperactive kid who runs impulsively into traffic, becomes a fidgety foot tapping adult = much less noticeable; the impulsive kid who leaps into risks, becomes an adult who can't inhibit themselves from impulsively interrupting or over-speaking =seems annoying rather than a clinical problem, doesn't it?
When you read that 60-70% "grow out" of ADHD, what is meant is that 30-40% still have an objective clinically significant condition requiring treatment. Obviously that's quite an external objective assessment, defining a somewhat arbitrary measure. It doesn't say much about the subjective experience of any individual. The overwhelming majority will have a subjective experience of cognitive differences. What's more is that this figure is rapidly changing with research, with greater understanding ever reducing the size of the group who are felt to "grow out" of it. Similar shifts have been seen over time with greater understanding of genetics -at one time the majority of ADHD was felt to be related the birth injury and environmental factors (blame the parents). I've watched over the years as the proportion of ADHD presentations felt to be inherited has increased 40%, 50%, 70%, 80%, 90%, 95%...
@Blackberriesbob
So many people, because it is so many people.
You may not care, and that's part of the problem.
ND children have been ignored for a long time. I'm old enough to have gone to school at a time when there were just those odd kids. The ones teachers shouted at and everyone else ignored or avoided. Or bullied them in playgrounds. Called them smelly or worse. And they gradually disappeared. Not everyone who started p1 came back for p2...etc. Then some disappeared out of mainstream education when it was time for secondary. I went to a tiny rural primary school and each class photo shows the kids who disappeared. And you know what, no one cared.
ADHD has always been understood as one of the most common childhood conditions, at a rate of 1 in 20. If you go into the history of paediatrics even 150 years ago there are reports of impulse disorders, disinhibition conditions. The name has changes, clinical science tells us more and more. But it has historically been given little attention in adults.
The current wave of awareness is not about fashion or identity politics. It's the shift to understanding ADHD as a lifetime neurodivergence rather than a childhood condition that the majority can ignore.
1 in 20 is a lot of people not to care about.