If you’re tiring of Eusebius, please skip along :-). I generally have the opposite problem: no posting at all!
Ἐνθάδε μὲν οὖν πνεῦμα στόματος αὐτοῦ ἀναγέγραπται. Εὑρήσομεν δὲ ἀλλαχοῦ καὶ λόγον στόματος αὐτοῦ εἰρημένον, ἵνα νοηθῇ ὁ Σωτὴρ καὶ τὸ ἅγιον αὐτοῦ Πνεῦμα. Ἀμφότερα δὲ συνήργησεν ἐν τῇ κτίσει τῶν οὐρανῶν καὶ τῶν ἐν αὐτοῖς δυνάμεων· διὰ τοῦτο εἴρηται· Τῷ λόγῳ Κυρίου οἱ οὐρανοὶ ἐστερεώθησαν, καὶ τῷ πνεύματι τοῦ στόματος αὐτοῦ πᾶσα ἡ δύναμις αὐτῶν. Οὐδὲν γὰρ ἁγιάζεται μὴ τῇ παρουσίᾳ τοῦ Πνεύματος. Ἀγγέλων γοῦν τὴν μὲν εἰς τὸ εἶναι πάροδον ὁ δημιουργὸς Λόγος, ὁ ποιητὴς τῶν ὅλων, παρείχετο· τὸν ἁγιασμὸν δὲ αὐτοῖς τὸ Πνεῦμα τὸ ἅγιον συνεπέφερεν· οὐ γὰρ νήπιοι κτισθέντες οἱ ἄγγελοι.
“Here we find ‘His Spirit’s mouth’ written, but elsewhere we find ‘His Word’s mouth’ said, in order that the Savior and his Holy Spirit might be known. For both were at work in the creation of the heavens and the angels. For this reason it says, “By the word of the Lord the heavens were stretched out, and by the Spirit of his mouth every one of his angels.” For nothing is consecrated except by the presence of the Spirit. Therefore, although the creative Word, the maker of all, prepared the way for the angels to come into being, the Holy Spirit, together with him, bestowed on them their consecration. For the angels were not created as children.”
I’m not sure what he means by the final bit “for the angels were not created as children.” It’s almost like αγιασμον (holiness or consecration) is functioning as a parallel to “coming of age,” since νηπιος can mean minor.
Alex Poulos, PhD 
Perhaps it refers to the fact that angels are made as they are, without birth or adolescence or growing to maturity, and so are ‘perfect’ from the start, contrast with human beings who are both born and sinful, and so our maturation must be both natural and spiritual. That would be my first take on it.