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I believe its ancient.  It takes Perfection a while to cook

Good point, Rick! Do you think that it existed on earth thousands of years ago though?

definitely ancient hiding some place in the depths of the universe waiting to be stumbled upon 

I think it is a matter of convergent evolution. In standard evolution theory it is thought that humans evolved from something related to apes, so through convergent evolution Xenomorphs initially evolved from something related to Deacons. However, through embryo implantation via facehugger, Xenomorphs then evolve by divergent evolution.  From this, I prefer to think Xenomorphs are an ancient species.

Ancient beyond a shadow of a doubt. I prefer to think that the Engineers or maybe someone before them, found a species akin to the original 'temple-builder-aliens' O'Bannon had in mind and harvested them for DNA as a Base for what would become Xeno/Neo/Protomorph creations. David could possibly simply have discovered this and carried out his own experiments with regards to such, aiming to Perfect the earlier work done many, many millenia previously.

Is it perfect?  Androids labeled it as so, but their concepts of perfection are likely vastly different than a living being (e.g. Kate Beckinsale is perfect LOL). Did Ash think it was perfect because he also wanted his parents dead and this would be a means to an end?  Or maybe Ash was crazy and violent behind his inhibiting code parameters and this beast was the embodiment of what he would be if he could?  But in the end, John Browning/Eugene Stoner and technology beat the creature, Which I find funny because Ash was born of technology and should have seen the inherent limitations of a biological being.

But to answer the question, it is ancient from a human perspective.  How long would it take humans to get to a point to even interact with these SOBs?  Centuries.

Hmm. Ash said it was perfect because of its structural perfection- which I suppose could be incorrect, but Perfect to him may have been more about the hostility, unclouded consciousness and lack of remorse and delusions of morality.

I agree with your summary of what he was thinking (processing?).  But he was wrong.  A tall, thin, untrained lady beat it.

I think it is everything, pre and futuro as well. However, the different types, neo/proto/xeno, should be distinguished in my op. The neo will be the revival of a natural ancient creature, I think. I see it as an original starting point. It would explain why there is only one city on the planet: it is forbidden to go outside because it is dangerous. The planet is forbidden but there is a garden where you can live, and this is the city.

Proto will be a human or android product, I think.

Xeno won't be explained in Covenant in my opinion, its story will be revealed in the sequels. According to Ridley, the sequels are about losing control of the creature.

The Deacon belongs to the Engineers/or their creators, I think. I would call them ancient since Prometheus revealed this fact by showing the mural, the head room, etc. Probably it is something engineered, so it is close to the Xeno technically, but obviously they represent two different lines.

And we are told that the sequels will introduce several new mutations, new morphs, so the family will get bigger and bigger.

To sum it up, the Neo (the spore-like earhugger) is the father.

The Deacon is the child of the Neo, engineered by the Engineers/other higher species.

The Proto is the child of the Neo, engineered by David/Walter. The Xeno is a more perfect version of the Proto engineered by... we don't know.

And the future Alien movies will probably reveal more children of father Neo.

Without any doubt it should be ancient. A nightmare and terror that haunts the universe. I imagine it originating from a biomechanical civilization that corresponds to HR Gigers visions. No ties to earth or humans whatsoever. However, I do prefer it being a kind of engineered species i.e. a bioweapon in contrast to being native to some ecosystem on some distant world. We cannot comprehend it's meaning or purpose since it is so alien to us and all we know. It should also be intelligent, but not in ways we understand. I think Ash saw these things and admired it therefore. 

Love the idea that the derelict ship carrying the eggs was a grown ship with the space jockey actually being part of the ship. The eggs birthed from pregnant wombs in the interior of the ship. It's been sitting there on lv-426 for not thousands of years, but millions of years, long forgotten, taking part in an interstellar war we know nothing about and never will.  

Definitely an ancient evil lurking in the darkest corners of the void

Ancient. And imho it is far from perfect as it gets its ass kicked by Ripley in the first movie. Moreover the whole hive gets wiped out by few and unprepared marines and Ripley in the second movie. It is an amazing organism but perfect it is not.

I like the idea of something ancient lying dormant and unleashing when awakened but also figuring out how to manipulate it- sometimes successfully, sometimes not.

The original xeno, as shown in the Prometheus mural, is ancient. The classic Alien xeno with it's biomechanical additions is from the 'future'.