I might have meant "real good", that is GM strength and up (2500+).
However, if we define "any good" as 2000, then, as you said, even that level is hard to reach at a later age.
My point is as follows: almost anyone can reach good strength in chess if they put a lot of deliberate practice at the early age(case in point, Polgar sisters). Conversely, at a later age, it is much, much harder to progress.
Put a 25 year old on an island for 20 years with only a chess computer and chess literature, and they are unlikely to make more progress that a 12 year old would make in 2 years.
Chess is not unique in this regard, in fact, many passtimes/sports/hobbies have the same limitation. However, I think chessplayers often prefer to ignore this facet of chess.
50% of adult chess players with a USCF rating (who already tend to be more dedicated to chess than most chess players, who tend not to have a rating at all) have a rating of only 1400 or below.
With a rating of 2400 you're getting up around the 99th percentile. You could easily crush virtually every chess player with a USCF rating. Of course, there are chess players who are even better, but they are the elite of the elite.
(Note: I wasn't able to find the equivalent FIDE rating information, so I have to use USCF ratings here. But you can bear in mind that a player with a given FIDE rating is generally stronger than a player with the same USCF rating)
