I don't have too much issue with the difference between the age of consent and the age of legal culpability. I think by the age of 10, it's easy enough to understand killing people is wrong or taking something which doesn't belong to you is wrong. There are other laws which aren't quite so clear cut, but then adults can struggle with that, and there's a whole legal profession to argue about the subtleties of these things.
The age of consent isn't so clear as right/wrong - some people are ready for it before 16, others won't be ready till a bit older. It's a pretty blunt tool as protection goes, because you can't really legislate for making people understand all the implications, physical and emotional and so on, of the decision to sleep with someone - enough adults screw that up, let alone teenagers who are just discovering all this sort of thing for the first time and feeling things they might not have any real understanding of.
But as has been pointed out, it's irrelevant when it's teachers. I'm not a teacher, but I do do some voluntary work which could involve me going into schools, and therefore I've been CRB-checked. It's been made very clear that if a school pupil comes on to us or anything like that, then just say no, even if it's a 6th former over the age of 16. (There are also guidelines on how to handle them confiding in you about any problems at home or anything else.) I don't really see how difficult it is to understand that. It's surely part of what you're signing up to when you decide to become a teacher - you're also deciding not to get involved with anyone you teach, and if you go against that for any reason, you know what the consequences are likely to be. It's not like anyone's moved those goalposts or made it unclear in any way. You're a teacher, you don't do pupils.
A few things in life are that black and white, and it makes it all a lot easier to remember that.