If tradeline has no negatives, then there is nothing negative about it assuming low util, etc. I still have an AU account from my parents from when I was 16ish. I guess I am still an AU on that account and never have bothered having it removed. The only annoying thing about it is that they have a reported balance on it when I am trying to do the 0 balance but 1 thing.
Various scoring methods may discount AU accounts and at one point FICO wanted to completely discount them. But they help to some extent so a positive account can't be a bad thing.
LIMITS IN CARD DESCRIPTIONS