But if their guess is 50/50, that is from a subset that is mostly under-60's, which presumably means that they have evidence for the opposite?

(i.e. there is no statement that the 51% figure is age adjusted)

I'm probably just being silly here...

I think they're saying over or under 60 is completely arbitrary when judging only from 'random' answers. It could be over or under a month, or 1000 years, the result would still be 50/50 because the ability to create a sequence that appears random has no link to age.

GP is saying it's even more than 50/50. Less than half of people are >60. A more extreme example would be if it guessed: "You are younger than 99 years old."

Yeah, 'We tried to work out the impact of age on randomness, and guessed that people were younger than 99 years old 50% of the time!"