DEAR MISS MANNERS: I just began a full-time grad program that is small, demanding — and excellent. I am 73 and my cohorts are in their 30s, and I haven’t noticed any particular gap in our views nor any alienation from the others. I am just absorbed in the reading, writing and discussions, like we all are. My concern centers on others’ reactions when they hear about what I’m doing, like: “Isn’t that wonderful! Good to keep busy! Keep your mind active! So important when you’re aging!” Nobody would ever say that to the other students. I’m taking this as seriously as they are. It’s not a little h…