I think it is much harder to prove age discrimination earlier in the hiring the process. E.g. when screening resumes. How would you find out the real reason when a particular resume fails screening? Thus the likely incentive for the company is to avoid older people as early as possible. This means older good candidates would fail screening more likely: in effect, discrimination.

It's so often forgotten that the intent of the law vs its actual effect could be in conflict.

The statistics themselves would indicate this. Which is why the lawsuit cites that the average age of a Google engineer is 29 vs the national average of 43. This does not bode well for them.