Freakonomics links to an interesting paper that looks at how defense attorneys and prosecutor utilize their peremptory challenges based on age.

[P]rosecutors are more likely to use their peremptory challenges to exclude younger members of the jury pool, while defense attorneys exclude older potential jurors. Having established that age has an important role in jury selection, the paper employs a research design that isolates the effect of the random variation in the age composition of the pool of eligible jurors called for jury duty to examine the causal impact of age on trial outcomes. Consistent with the jury selection patterns, the empirical evidence implies that older jurors are indeed more likely to convict.

Is there a Batson-type challenge for age discrimination? I know it covers race and gender.