Citation? I flipped through a few articles on Wikipedia but didn't see anything

Oscar Wilde's personal life with teenage boys

There's an episode with a young boy in A Rebours, a little googling says chapter 9

I don't think there's a canonical age for Salome's seductive dance but she's often like 12

A decadent work not mentioned here is The Immoralist by Gide, where molesting young Arab boys is much of the plot

The trick seems to be to rebel against the conventional in a way that's perpendicular to it, not merely —as most rebellions are— a sign flip?

Yep. If it’s a sign flip it’s not really a rebellion because it’s operating from the same dysfunctional paradigm.

I feel that it is important to point out to native english speakers that the word "decadent" shares a root with decay, and simply means a decayed rotten state, a decline. It is perjorative. There are no implications of 'opulence', unlike the common usage of "decadence" in English as a sort of slang to describe a rich chocolate cake, for example.