I am interested in modern AmE. For instance, when John and I studied in the same university before, when someone asks who John is. I can tell the questioner "John is my school mate or school fellow." I know there are alumnus and alumna, but they are either for male or female.Please give us the complete sentence, jokaec.
Neither "school mate" nor "school fellow" is used in modern AmE. "School" most often refers to primary and/or secondary education, not college, and certainly doesn't distinguish one from the other. We have a few terms with "mate" like "classmate" (someone in the same class/year) but very, very seldom would we use "fellow" in that way.
Thank you all. Do you mean if I say "John is my alumnus" and it's wrong?Both "school mate" and "school fellow" (with or without the space between the words) sound odd to me, and I would never use them. (And while alumnus/alumna are wrong for your sentence, I'm not sure why you see the gender specificity as a problem, as you presumably know whether John is male or female.)
I would just say "John and I went to college together" or "I know John from Princeton" (if Princeton is the school in question).
[Cross-posted with Myridon]