In America, there are laws, then there are the actual implementation of those laws, follow by the interpretations of those laws, and finally the bottom line, which is that you get just about all the law you're going to get in proportion to the money and the quality of the legal council that you so engage. When Congress passed the Age Discrimination in Employment Act of 1967 (ADEA),the purpose was to protect those age 40 and above from employment discrimination, because the bottom line when it comes to employees, is that younger employees are in general cheaper in labor costs, cheaper in health costs, have less family issues to attend to, and typically are more moldable by the employer, so if you are needing a lot of "Indians" but not so many "Chiefs", younger employees typically provide such a benefit.
In addition, because younger employees have a very strong tendency to exert downward pressure on labor costs, it makes it difficult for older employees to make all the money that they deserve to make, and if those older employees, know that finding another job with the same pay and equivalent benefits is more problematic for them, that makes them far more quiescent in pushing for higher pay rates or benefits.
Although, America does not have a law that stipulates that you cannot ask the age of an applicant, most employers as a matter of course do not do so, because that is almost prima facie evidence that they are walking the path of potential age discrimination. Rather, and I suppose they think they are so clever, they work around asking the straightforward question, by sometimes requesting a picture to go with the online resume, which can open up an entirely new can of worms, or the favorite, which is for the applicant to place on their resume or follow-up questions, the year that they graduated from college.
The thing about the graduate year is that knowing such, doesn't mean that you know for a certainty that someone that graduated in 2015, is in the age range of 23-27, as there are older people that don't get around to finishing their education until much later in life, yet there is a reasonable presumption that most graduates at that time are young, whereas for those that state that they graduated in 1985, there is an absolute certainty that they are over the age of 50, and cannot possible be in their twenties.
Further to the point, since most resumes are now uploaded online, it is very easy for an independent party to create a program that takes those dates and segregates out those that are older from the desired targeted candidates without such a procedure actually being divulged to the client. Rather, they might say, that the sophisticated analytics that are applied to resumes only produces the best candidates for further review. Whether this is true or not in actuality, misses the point, the point is that graduation dates are especially for companies receiving boatloads of resumes a very easy way to separate out those that they have no real interest in interviewing, further if they have some sort of plausible denial in place, no one is the wiser. Does it happen? No doubt that it does.