I was told that carbon dating is innacurate. My friend claims that carbon dating was used on a-?

recently spewed out piece of magma that had cooled. He went on to say that the CD method innaccuratly claimed that the magma was thousands/millions of years old or such. I would like to refute this but I can't find any information on this. This is all part of a debate we have on evolution vs. creationism. Any information on the accuracy of CD and perhaps the case that he brought up would be greatly appreciated.