That's a valid point. Although I'd add that, as you get older, it's not only the significance of the stimuli that increases, but the overall levels of stimuli increases. More responsibilities, more burdens, more stress, and less likely to be given any concessions due to being young.

No, it gets worse. Adults don't have the amount of mental plasticity that younger people have. While it's possible to make things easier through CBT and learning to cope and deal with certain challenges. The mental load of keeping up with daily life ultimately has its toll. Life is getting harder every year for everyone, and having ADHD makes that mental load just that much harder.

Realistically, it's utterly dependent on one's life situation.

When you're in school, your main focus is trying to get through school, get home, and not get hassled about keeping up with yourself and your things.

Later on, some jobs, are congruent or even complimentary with symptoms, some jobs aren't. Some partners help compensate, some don't.

It absolutely will get worse for some, better for others. Some may have consequences that are an issue, some may have circumstances that defuse the consequences.