Given the authors I'm not surprised- they've been against all sorts of pandemic measures including the vaccines and testing.
They repeatedly conflate mandates with masking efficacy. They don't distinguish by mask type. No discussion of adherence.
You'll spot in this piece a lot of mention of "reanalysis" of awkward studies and evidence against their conclusion. That reanalysis was unsurprisingly done by the co-authors.
Also they claim masking harms- again using papers by the co-authors. No mention of counterevidence for that claim.
I don't see a particular reason to exclude older ages after 18. We don't have RCTs of children, but we do have them for adults. Likewise with the other evidence. In their absence, I don't think the correct move is to therefore to conclude "the current body of scientific data does not support masking children for protection against COVID-19." It is to note their absence, but mention the evidence for adults and the ways that evidence may or may not be similar.