Barring really simple stuff like boiled eggs , are there any really old dishes or recipes that have been around in one form or another for a really long time?
It's impossible to say what the oldest extant recipe is, because you're looking at pre-history. We can find evidence of foodstuffs in preserved tomb environments but that is somewhat self-selecting evidence in that it falsely indicates that the oldest recipes are those using ingredients that survive for a long period in those environments.
That said, the items which we have good evidence were being used a very long time ago are generally alcohol and grain foodstuffs (as dried grain survives well in arid environments, and analysis of chemical and pollen deposits can usefully identify mead or wine). Likely contenders are mead, wine and variants of modern beer although they would likely be slightly different from modern versions. All were certainly used in Egypt, 3000-4000BCE.
Ritschert is an Eastern Alpine stew made from barley, beans (or peas, lentils), and smoked pork meat.
Archaeological excavations in Hallstatt salt mines prove that Ritschert was already known in the Bronze Age. Remains found in preserved cooking ware contained beans (Vicia faba minor), barley, millet, pork meat, and wild garlic.
Source, incl. reconstructed original recipe (p. 10; PDF, in German).
Follow up question: what were the oldest breads like? There are so many varieties of bread from all over the world - are any of them particularly like things that would have been eaten thousands of years ago?