"Old Age" is one of my favorites.
Nirvana is also my favorite band of all time,I saw them live in 93' at the civic center in Lakeland Fla.,they rocked. 
BTW,I do think he killed himself,as I know how suicidal heroin addiction can make you from first hand experience. I have heard all the conspiracy theories and they are plausible but i'm not sure what to think. Guess we will never know for sure.