I have a colleague with whom I am friendly. Nay, I would go so far as to say we are friends. She is a lovely person, a great scientist and a committed human being: caring for family, friends and the students. When my Mom died, she was very supportive at work. I have tried to be supportive of her issues in balancing life & work (I say "try" because I cannot judge what was useful or not for her. That is her call). I have certainly read many grant proposals and helped with those.
As you can guess, there is a but coming.
Every time this woman sees me she says something like "are you OK?" or "you don't look so great, is something wrong?". The fact is, nothing is wrong. I am old. When I get tired by the end of the day, I look tired. I don't think I am more tired than I was when I was 30. But maybe I am. I think that we (as a society and culture) think that looking old often equals looking tired, or looking ill. But, in truth, I am probably less tired, because I am getting better at making sure I get enough sleep and eat well and take care of myself.
I am not sure of this, and I'm certainly not a fixed perspective, but I think things like "tired" do show more on old faces (as opposed to actually being tired). There are things one is better at hiding as one ages: disappointment, for example.
There are times when I have thought older faces are more interesting than younger faces. But then I teach and young faces, when engaged in something they want to do, engaged in something difficult, engaged in learning something they have chosen are as variable and interesting as any set of other faces. Stay away from magazines filled plastic people (usually young). Stay away from news announcers and TV programs where it seems like botox has erased the subtleties that make each human being unique.
When people talk about teaching being invigorating, there may be lots of reasons. Sometimes it is the information and the flow of information. Sometimes its working with other people, different ages, and seeing them grow right before your eyes. Sometimes its just being reminded as to what being human is.
No I'm not tired. I just look like the old person I am. And I am proud of every damn wrinkle, scar and yes, I'm even getting warts at this point.