I feel like if the situation had been reversed and it was female teachers and male students, there'd by a bunch of posters complaining about how terrible the student who tattled on them is.
I don't know how old they are specifically, but myself and friends of mine have been flirted with often and openly at various locations by girls who can't be older than 20. We laugh, say we're too old, they ask, and we're honest. It doesn't matter to them at all. In fact I think some are actually turned on by it in some way, or seek it out even. I'm in a happy relationship with my gf of 4 years (she's 27) and I'm not interested, but it's flattering and fun just the same.
This is in Quebec btw... so I do have to say it's much more liberal and open-minded here. Relationships with decent age gaps aren't all that rare, shocking, or offensive to most people, and certainly not worthy of jail-time or arrests. USA is nuts with that shit.
The same 17 yr olds that liked the Backstreet Boys, they weren't exactly teens when they were popular with my age group (and I was like 11 at the time they were popular).