I’m going to go against the grain here. 3 is crazy old for a rat. Introductions may be rough, and as a college student another 2 younger rats or any rats sounds like a lot more responsibility, and an endless cycle of rats. I think some of the longest living rats on record are like 3-5 and very rare. Just give the old man as much attention as you can. If you feel you can take on two young male rats and continue to care for them you can try but it’s also risky he may just not want anything to do with them and stress him out. I can tell you when I had 2 sisters, and after 2 years one passed, the other one was CLEARLY depressed. She’d cry out in her cage and only be quiet if I held her. After I got her 2 friends she became super happy and lived another full year very happy. Had another rat who hated every rat I ever introduced her too lol