Hmm, your post made me wonder so I looked up the law itself. I won't cut and paste the entire thing here since it is extremely lengthy but I will do so for the applicable area. There are a few exceptions, ie, since there is an age limit for an ATP that would be "legal" age discrimination, but as far as I can tell the law offers protection to all ages, not just old people. The reason for the law was because of discrimination against older people, but all groups seem to be protected.

Is there something buried later in the law, or more recent court cases which I'm missing which allow an employer to discriminate against younger people?

(a) Employer practices

It shall be unlawful for an employer-

(1) to fail or refuse to hire or to discharge any individual or otherwise discriminate against any individual with respect to his compensation, terms, conditions, or privileges of employment, because of such individual’s age;

(2) to limit, segregate, or classify his employees in any way which would deprive or tend to deprive any individual of employment opportunities or otherwise adversely affect his status as an employee, because of such individual’s age; or

(3) to reduce the wage rate of any employee in order to comply with this chapter.

(b) It shall be unlawful for an employment agency to fail or refuse to refer for employment, or other*wise to discriminate against, any individual because of such individual’s age, or to classify or refer for employment any individual on the basis of such individual’s age.