Humanity Is Young

"Yeah, I've heard about humans — think you're the center of the universe."

So, you're a human, and you've just met a never-before-seen race of extraterrestrials, and chances are you feel quite insignificant compared to the hyper-advanced culture in front of you. Often, the species will appear Younger Than They Look, in order to make the surroundings feel more comfortable. The being will then kneel down in front in you and say, in a gentle, soothing voice something to the effect of "You humans are so young, yet in your short lifetime you have accompanied so much." In other cases, when confronted with multiple races, one group, usually a Five Man Band, will be willing to accept the human, while the rest of the race dish out doses of Fantastic Racism. Contrast Earth Is Young, where the planet, not the species has been in existence for a short time, and We Are As Mayflies, which is about humans being young as individuals.

Examples:

In The Movie of Green Lantern, Tomar-Tu calls Hal Jordan's species young, trying to encourage Hal to prove his worth to the other Lanterns. The other Lanterns, and the Immortals, however, see his humanity as a weakness and treat him as a member of a lower caste.
- This is especially bad writing because there's no reason for most of the universe to have heard of us at all--we're not really spaceflight-capable even for short range, and the movie is set in the very early days of the superhero era. Unless it's supposed to be after the Fantastic Four movie and the rumor got out that we kicked Galactus' butt, we should be just one of those races nobody's ever heard of, and instead they had negative opinions. Which Ryan Reynolds tends to affirm.
- Green Lantern has always been a franchise that treated the universe as being incredibly small, anyway. A sector lantern has oodles of galaxies under his care, and yet most seem to spend the vast majority of their time defending one planet. Every Green Lantern who's ever been an active member of any Justice League incarnation (except Alan Scott, obviously) is guilty of gross dereliction of duty. So many mass extinctions while John Stewart was keeping order on his homeworld...
In the Transformers Film Series, this is the sole reason why Optimus Prime must protect the humans, and why Megatron must destroy them.
Q in Star Trek the Next Generation. Although he tends to lean more towards borderline Fantastic Racism, and thus has to conduct the ever-increasingly difficult tests in order to prove, quote, "humanity's worth".
- As are the Vulcans, but with Fantastic Racism that declines from Star Trek Enterprise to Star Trek Deep Space Nine.
In Babylon Five, humans are relatively new to interstellar travel: The first other race they met was the Centauri (who were, from the interstellar perspective, the ones who discovered them), and the Minbari have reportedly been a spacefaring race for millenia.
In Mass Effect, humans are one of the most recent races to make first contact. Also overlaps with Humans Are Diplomats, since we're also essentially taking over the universe.
- Ask the other "older" races, particularly the Batarians, and they may instead say Humans Are the Real Monsters
The termites of Professor Mmaas Lecture state humanity to be a species as young as a nymph (termite young).
In Animorphs it is noted that humans are a lot younger than other species. Ax, however, expresses astonishment at how quickly they manage to do things; apparently it took his species three times as long to get from heavier-than-air flight to space exploration. (Another book reveals the primitive version of his species were around millions of years ago, and also that the Ellimist gave them their boost to sentience.) The Howlers are also mentioned as being thousands of years old but more or less stagnant, which makes sense if you know their origins.