Predator RaceHow long they've been around is something no one may ever find out. It's one of those things that never get answered.
As for Aliens being intelligent...
Maybe Predator fans (hell, anybody who has seen the movies but aren't a real fan) may think that Aliens have no thoughts at all, and are just brainless killing machines. I'll tell you something.
THEY'RE WRONG.
Of course the Xenomorph species is intelligent. They might not be able to talk, making them dumb (yes, for those who don't know, the real meaning of dumb isn't stupid, the meaning of dumb is not having the ability to talk), but they sure as hell know what they're doing, and they can plan it out as well.
Take this example from Alien Resurrection... the three Aliens trapped in the box "discussed" what would happen next, and they sort of devised a plan of how to get out of there. Killing the runt of the three, the acid from the body was used to escape, thus making humans scared like a little kid is to the Boogyman.
The Queen, being the most intelligent of the species, doesn't just pick a spot and starts "laying" her eggs. Well, you know what I'm trying to say.
The Warriors in ALIENS seemed senseless at first, but as you see further into the movie, they actually tried to ambush the humans (and various other things)- being as human as the humans were, they had a motion senser handy and were able to counter this.
The Superfacehugger of Alien 3 (very beginning) waited for the right moment to strike.
I think that, the most disgraceful of the entire Alien species was the Queen in AVP. Not only did she look like she was signifying she was free to the humans by running mindlessly through the halls and stomping like it was the 4th of July celebration after-party, she attacked head on without really thinking of the consequences.
Second to that was the Newborn. Not only do I hate it more than year-old tuna casserole with a side order of moldy fries dopped in oatmeal, but it just plainly speaks for itself, with its look, its acts, and most of all, its look.
I am a Machina-Alien! (Mok-In-Uhh)"To me, everyone is crazy. The ones in the mental house just got caught."