Just say "another student". It should be enough, and it's not disrespectful to them in any way. If you have to clarify, say something like "John help me with this project: he's in his fourth year."
I'm Korean, and my language also makes that distinction all the time. When I joined a graduate program in the US, it took me some time to adjust: I'm a first-year student, here's another guy who joined two years ago, but we can be friends! Unthinkable in Korea.
It is very unfortunate that my native language (and social custom) forces one to make such unnecessary distinction all the time, and it sounds like the Chinese language also does it to some degree, but for some reason, English does not have this particular problem, and there's no reason to import the unnecessary distinction into English.
(If I sound too preachy, consider a more neutral situation: imagine a language that makes distinction between male and female doctors, and one asking, "I want to say 'I went to see a doctor.', but I want to explain the doctor was female. How do I make the distinction in English?" The correct answer is: you don't, unless the doctor being female is somehow relevant, in which case you can simply say "The doctor was female, by the way.")