Is derilect ship older technology?

We have F-16's and bombers, helicopters,etc,there could be multipe alien craft ( such as the hovering disk ) or one craft could be hundreds or thousands of years older, or suited for a different function. They are supposedly bio mechanical so they can easily transform in accordance to needed functions possibly. I think you have various ships and possibly various times that we are beholding the engineers. What if the engineer that we see outside on the surface of the planet looking at his hand is simply old and he or his race is dying. He could be creating or terraforming earth, seeding earth with the beginings of man, and then enters his ship, leaves and either hibernates until his creations fullfil their potential to make contact with their race to be host to his races DNA (immortality in a sense) and he comes back to earth to repopulate his species. And as far as the Derilect ship discovered by the Nostromono in Alien, that could be a engineer that escaped off the promethius planet heading to earth to invade, or just trying to get back home or quarantine himself because he knew he was doomed and just headed for the most desolate location he could find before what nappears to be a chest buster got him and he crashed. Maybe he's a larger benevelont jockey and the ones encountered by the prometheus crew a smaller more aggressive species that infected him and turned his crew to all those eggs (Dallas cacoon scene where he was being transformed into a face hugger) If there is a 30 year difference as stated between Prometheus and Alien that derilect ship could be old alien/space jockey technology, because the movie, screenplay and books seem to make it ancient, maybe thats why you have eggs and no steel looking cylinders.