Re: What would you do? (Older male teacher with young female student)
The law depends on age but also on whether the older person is in a position of authority or trust.
But it's true, if you're disappointed no one else did 'something' (talk with her parents, discuss with police or other authorities and ask them for advice), the exact same question applies to you as to any other adult there. If there was something potentially harmful happening to a child every adult who suspected it but didn't do something - which of course includes you as much as anyone else - is jointly responsible.
Diffusion of responsibility is often a culprit when people need help and no one helps them despite multiple people seeing -- everyone assumes it's someone else's responsibility to 'do something'.
OTOH, if the young woman was an adult unless the relationship was abusive it's not really anyone else's business. I might find a 30 year age difference very off-putting but so what? It's her life, not mine or yours. We're all free to live our own lives as we choose.