I remember a court case--can't recall the state--but it came down to a young employee who sued because the state law didn't specify as hr410 mentions. But the court said that the language of the law was intended to mirror the ADEA, so the employee lost. So, it might not just depend on wording of the law...
I had a friend who complained to me that she believed she was having a hard time getting hired because of her perceived age.
While one is tempted to defend an employer's right not to hire someone who is young b/c the employer may equate youth with inexperience, it IS considered wrong not to hire someone who is older b/c the hiring manager may equate old age with any number of things such as: stuck in their ways, not proficient with computers and other technology, etc. It's also considered wrong not to hire an older person because you want the company to have a "younger image".
So, really, it seems that younger people perhaps should be protected by laws prohibiting sex discrimination--it's no more right to make assumptions about someone due to their age (or their perceived age based on observation) than it would be based on race or gender.