Ask 100 people off the street to define "rich". How many of them will make "for their age group" part of that definition or even mention it? My guess is fewer than 5, possibly 0.
The problem here is that "rich" has always been a relative term like, "tall". My four year old is tall, for her age, but she is still short. My wife is tall, compared to all adult women on Earth, but she is still short compared to me. I am 6'4" and think of myself as tall, but I am short for an NBA player.
So if you were to ask me "are you rich" or "are you tall" I can't really answer that question without providing some context. Yea, I'm guess I'm pretty rich, but I'm not like RICH rich. I know a ton of people who are waaaaaay more rich than I am, and my net worth is much closer to zero than it is to their net worth, so to them I am not rich. A grown man who is 6'4" and a grown man who is 5'8" are almost indistinguishable to Manute Bol, who towers over both of us by more than a foot. My daughter and her classmates are all short to me, despite having an acute sense of who among them is tallest.
So let's go easy on the "who is rich" question for a while. The context absolutely matters, and I understand why people who are objectively far richer than average, compared to the planet as a whole, still feel financially insecure in America.