Old age doesn't automatically mean technological incompetence anymore.
For example, Judge Alsup was born in 1945 and demonstrated a perfect understanding of the issues in his ruling. As I recall he even taught himself Java programming during the trial.
The problem is the reprehensible ageism inherent in claiming older people are not capable of understanding technology. The same ageism you are implicitly supporting by "reassuring" us that young people (hence, magically tech-savvy people) will have input.
A bit shrill, I think. I don't think it's ageist to acknowledge that a lot of technologies didn't exist when older people were born and, thus, they are less likely to be familiar with them. That doesn't make them dumb, it's just an accident of history. And certainly I think that a good lawyer (and amici) should be able to explain anything the justices need to know -- the justices, whatever else you may think about them, are very intelligent people and surely capable of understanding just about anything, given sufficient time, regardless of their age. (Though this time caveat is a significant consideration. Overcoming that restriction is largely what clerks are for.)
None of this is inconsistent, though, with it's being beneficial that there are additional very smart younger people, who may be more likely to be familiar with newer technologies just in case their perspective becomes relevant.
Why is that a problem? It's certainly possible that the judge was an avid home computer enthusiast in the 1980s and knows about tech.
Old age doesn't automatically mean technological incompetence anymore.