Having worked in the past with an oil manufacturing company, I can say that there is no technical need to change the oil every 6k miles - it will easily last for 30k miles and will not degrade. Changing the oil twice a year is a complete waste of time. Don't worry about your oil being old, it won't have done any damage.
However, changing the oil filter regularly makes more sense, as it will collect any particles and bits of crap that are floating about. But only really an issue if they clog up and reduce oil pressure - highly unlikely.