@meinburn it's more excusable when both are adults, since they both likely know better by that point- but it's still kinda creepy and not without complications. Dating someone that could potentially be their daughter or son, for an example, is bound to have a large difference in maturity levels and life experience- it's hard to say someone with vastly more life experience isn't taking advantage of the other in some ways, intentionally or not. Taking advantage of their physical youth, taking advantage of their inexperience, taking advantage of their place in life.
An example- An older woman who has a house, plenty of money and security, being in a relationship with a kid half her age who has nothing but a high school diploma, the clothes on their back, when they moved in with her. How is that NOT taking advantage of the kid in several ways, whether she intended to or not. Heck, I don't see how that wouldn't stunt the kid's growth as a person or how she wouldn't directly control their life in several ways, again, intended or not. The creepy part comes from things like being an adult before the other person even existed- or while they were in the crib- there's a reason cradle-robber is a term and has a lot of stigma attached to it.
The gap grows wider as you get older for what is commonly considered fine, and not all things are absolutes when it comes to love and relationships- like it can work out, sure. Maybe the older person is very immature and in a similar life situation and the couple grows together, it can happen- but in most cases it's just a bad idea. Not to mention the problems that will occur later in life when the older person in the relationship starts suffering the problems that come with old age long before the other person (and likely dies long before the other, leaving them alone).
A teacher dating a kid? No. That's never alright. If you're in primary/middle/high school you're still a kid. Heck, even most people that graduate still have the maturity of a child. People just look at it as a number, but there are more factors than age. I find it bewildering that so many people either can't see these things as problems or willfully ignore it. What's the defense for a "high school" teacher dating one of their students? Because someone thinks it's hot? It's a work of fiction so who cares? It's ironic I see someone here mentioning Nazis, cause ya know, that's exactly what happened when people just ignored things that were morally wrong.