Meadmaker: And of course, age might play a role.
But I have to chuckle to myself when someone who is about 20 years younger than me thinks he is getting too old and befuddled to play chess well. I know one guy here (who has me blocked) who makes a career out of blaming old age (he's only 61 and talks like he's 80) on his feeble chess skills.
I think mostly what is going on is that if one is a lousy chess player later in life, they were probably a lousy chess player when they were young..
Certainly people at age 49 can be great Chess players. However, can they learn to become great Chess players? I don't know. For my part, I was not a lousy Chess player when I was young, because I was not a Chess player when I was young. I knew the legal moves of the pieces, but I will bet that prior to my 45th birthday, I had not played 100 games of Chess, and 90 of those were between the ages of 6 and 18.
While we don't like to face it, age does not make our minds more open to new ideas, or to new skills. I am most familiar with this in the field of language acquisition. The ability to acquire a new language drops continuously throughout life, to the point that it is almost impossible to become fluent in a new language if you are not at least conversant in it by the time you are 35 years old. Those people who are the exceptions that prove the rule have to be very dedicated and put in an intense amount of work, far more effort than the 12, 16, or 20 year old sitting next to them in the classroom.
I have to wonder if learning Chess skills is comparable to learning a new language in that sense. If you learned it as a child, it can come back to you, and you can build on your skills, but what if you never learned as a child? I can't say, but it doesn't seem outlandish to think that, just as you will never speak Japanese fluently if you try to learn at 40, you will never play great Chess if you start at 40. Or, if you can, it would only be through an insane level of dedication. Some counterexamples would help settle the question.
I do know that the attainment of grandmaster skills during middle age was sufficiently remarkable for GM Ben Feingold to make the cover of Chess Life as "the 40 year old grandmaster."
Good one! (lol)
Now, if (hypothetically) a high IQ doesn't necessarily correlate to a high chess competence, then that would suggest a low IQ doesn't necessarily correlate, either.
I think that most of us know that study/training, application/practice, patience/time are prerequisites to success at chess.