I knew I'd missed another recent example!

And yeah, when it involves teachers and students, age-gap relationships take on even more red flags. Like you said, there can be non-predatory ones, but not when they involve someone under (and someone significantly over) 25 and/or a power imbalance like that between teacher and student. I'm always creeped out when I find out professors have married their grad students or TAs. Such a creepy dynamic.