There are at least two references that occur to me. One is a tablet from Abdu’l-Baha at http://reference.bahai.org/fa/t/ab/MAS2/mas2-88.html
, which says more or less:
Each one of the heavenly stars is a special creation (or creature,
khalqii). This terrestrial globe, which is in comparison infinitely
small, is not empty and futile. What then of those exalted, luminous, enormous bodies? And this is clear in the Quran, which says "Among his signs is the creation of the heavens and
the earth, and the animals that disperse in them." (42.29) It says, "in
them" and not "in it." It is clear that there are creatures possessing
breath in both, because animals that breathe, move.
Then it goes on to talk of the 24 elders in the Revelation of John,
and I wonder whether the original question put to Abdu’l-Baha might have asked about a relationship between planets and elders, or elders and Bahais. Or were there simply two unrelated questions?
Note that breath and spirit are the same word in Hebrew, Arabic and Persian. I translate it here as breath rather than spirit, because it is linked to movement, the thing that distinguishes the animal kingdom from the plant kingdom.
The second is from Baha’u’llah
Thou hast, moreover, asked Me concerning the nature of the celestial spheres. To comprehend their nature, it would be necessary to inquire into the meaning of the allusions that have been made in the Books of old to the celestial spheres and the heavens, and to discover the character of their relationship to this physical world, and the influence which they exert upon it. Every heart is filled with wonder at so bewildering a theme, and every mind is perplexed by its mystery. God, alone, can fathom its import. The learned men, that have fixed at several thousand years the life of this earth, have failed, throughout the long period of their observation, to consider either the number or the age of the other planets. Consider, moreover, the manifold divergencies that have resulted from the theories propounded by these men. Know thou that every fixed star hath its own planets, and every planet its own creatures, whose number no man can compute.
(Gleanings from the Writings of Baha'u'llah, p. 162-3)
The topic here is obviously astrology: the influence of the spheres on “this physical world”. But there is also a reference to people like Bishop Ussher who dated the creation to 4004 BC. He produced dates for the main Old Testament events and these dates were sometimes printed in the margins of Bibles. Baha'u'llah is saying that the creation could be much older than the earth.
The crucial phrase at the end of the quote is an Arabic insertion in an otherwise Persian text.
wa le-kulle thawaabetu siyyaaraat,
wa le-kulle siyyaaretu khalq
and to all the fixed-ones [are] travelling-ones
and to all the travelling-ones [are] creatures.
Because of the change in language, this might be a quotation from some Arabic source or saying. Baha'u'llah often refers to things that were "known" in the Islamic sciences (alchemy, history etc), and some of these things have since been disproved.
I've never heard anything about communication with aliens as a sign of maturity. I'm fairly sure this is just part of the oral lore that circulates in the Bahai community. David Piff wrote a book about this, and collected hundreds of examples, some of them quite funny. It's called "Bahai Lore" and its published by George Ronald publishers in England.