The general is that income, like wealth, is correlated with age, not ransom. Most workers under 18 will be making near minimum wage. Workers in their 20s are probably still starting their careers. People fall off again when they are older, as they either retire early or in some professions just become less capable.

So when you put it all together, a lot of people with an under average career will have an over average income at 35: Just not an over average income within the cadre of 35 year olds.

The lack of correlation with income at 20 comes from how many careers require training that doesn't give good early income. A future doctor, barista or AI programmer are not likely to have. a great income at 20, but their incomes and wealth diverge rapidly as some have longer training with different outcomes. The doctor will hit the 1% after residency. The AI expert might start making money earlier. The barista is probably ahead in his 20s, but it's unlikely their income grew quite as much, although many a barista is working on doing something else. So again, looking just at percentile of income at different ages is going to lead to mistakes as different life curves are being aggregated together.

Yep. I have responded in another post with some stats/surveys. Exactly, the aggregation of people hides the trends, and the fact that a 35 year old is not competing with other 35 year olds, but also with other 21 year olds working at cafes, contributes to this.