I'm the same age as you, and I had my grandma cosign on my loan for my truck. I wouldn't have been able to get it with her or another relative with good credit. As long as you have a job and you can prove that you can pay the loan you should be fine with a cosigner. By the way, I love my 2002 duramax, had it for almost a year now, and it still runs great, no problems. If you can figure out when the injectors have been replaced last, that would be a good guide on whether to buy the truck or not. If the injectors haven't been done in the last 50k miles, i'd steer clear.