Very true in my experience. While many (maybe 60%) still have an account, they basically do nothing with it. If you're a Facebook employee you may see that number of signups number and go "yeah they are using it" but the amount of use is VERY different from what I can tell.
Generally I'm very in agreement with the parent: The older won't want to use Facebook for dating, the younger would never look to Facebook.
That said, I'd go even farther and say the original claims are offbase here. First, teens absolutely have multiple personas they show, but they tend to be privacy circle based in that there are maybe 3/4 levels and they share increasingly more/less with each level.
Not only that, Facebook knows this. Instagram launched "close friends" explicitly because everyone was using "sinstas" and "finstas" to post to a smaller subset of people.
To me, all of this says that Facebook is probably targeting an older market of maybe say Match/OkCupid users who aren't used to a type of Hinge style interface. Anyone I know on Hinge would laugh you out of the room if you asked them to switch to Facebook dating.