Gosh, re the teacher and students issue, I must admit that if I were a teacher of teenagers (as opposed to young adults) I might be too terrified to risk trying anything new. I deeply admire you if you have the courage, and totally understand why you might think twice!
On the subject of wearing things that are marketed at the young currently, which is a different issue from the one above (for me at least), if we all rigidly stick to what we think 'the rules' are for our age group, how will fashion and style ever evolve? SOMEONE has to have a new idea or try something new of else the whole thing grinds to a halt. Change is an essential feature of fashion.
Whilst there is a definite grain of truth in the idea that young people can wear just about anything and not look ridiculous, whereas older women trying to wear various things can easily look ridiculous to current eyes, the more older women actually wear things they like even if some people will think they look ridiculous (because no matter how boringly you dress, someone will always think that you look ridiculous), the more everyone will adapt to the idea of older women having fun with fashion, and the less ridiculous we will look.
Ideally, at least in my view (and as I said, I would be too terrified to even think of wearing anything interesting to work were I a teacher of individuals under the age of 18!) alleged age appropriateness should be very low down on the list of criteria by which we judge our outfits, because age is not in itself about the individual person. Even climate has an element of choice for those of us in the Western world, but age does not. Many individuals would change their age if they could, or at least undo age-related physical damage, and many individuals do not feel like a different person when they are older, so if you want to dress in a way that feels authentic for you as an individual, and you, that individual, feel pretty much the same as you did when you were younger, then dressing putatively age appropriately is likely to cause you to be dressing inauthentically for what really matters: you, the individual, the person, with your own unique personality, values and ideas.
What you wear is about how you present yourself to the world as well as how it feels to you, and if you dress according to allegedly age appropriate guidelines, what you are communicating is your age rather than about you, the individual. What is the value in communicating an accident of birth that you have no choice about? I don't want to suggest that we can completely disregard age -- we live in a society and that has implications and effects -- but I do think it is worth asking ourselves whether such-and-such age-appropriate 'rule' or 'guideline' is something we want to follow or break. The more 'age-appropriate dressing' rules and guidelines I read about or hear, the more arbitrary and ridiculous many of them seem to me.
Whether you choose to follow them or not depends on how invisible you want to be, as much as anything else. Those who enjoy invisibility will want to adhere to all the rules. (You still have to keep up to date though, because they change over time no matter how much people think they don't.) Those for whom invisibility is not one of their style aims may want to experiment with breaking the 'rules', especially in cases in which they have a hankering to wear a particular thing, as in this case of the fedora.
Oops, sorry. Got carried away there! (It's my age you know.)
Have fun, however you handle the 'age-appropriate guidelines' issue.
