In the New Testament the Greek word ‘prototokos’ is found here: Romans 8:29, Colossians 1:15 and 1:18, Hebrews 1:6, 11:28, 12:23, and Revelation 1:5.
Luke 2:7 refers to Mary giving birth to her first (‘tikto’) son (‘gennao’). Gennao is the bringing into the world of a separate entity, a unique individual, a new life. In the case of natural childbirth, ‘gennao’ occurs after ‘tikto’. However, the use of ‘prototokos’ when applied to Christ Jesus (six times, in the singular) takes on a far greater significant meaning.
Firstborn does not mean first created: The Greek word for firstborn (Prototokos) in the New Testament means first in rank, an heir, to have pre-eminence in position, NOT in origin. The other Greek word for created is Protoktisis; it is NOT used for Christ. Since Jesus is self-existent (not created), the Holy Spirit had the Apostle Paul use the word “prototokos,” not “protoktistos”. Full explanation given in 
Another source  has this to say with regard to the meaning of prototokos as it applies to Christ Jesus:
The context of Colossians 1:15 and the phrase in which we encounter prototokos should weigh heavily in our interpretation of the word. Many would disagree with the interpretation and above definition due to the connection of prototokos with pases ktiseos. These would interpret this phrase as being a partitive genitive, making the prototokos a part of creation, a created thing, rather than superior over all things. It is admitted that this could be construed as a partitive genitive, but this is excluded by the context, which sharply distinguishes between the Son and ta panta, and for this idea Paul would probably have used protoktistos. The well-known scholar, A. T. Robertson, wrote:
“The use of this word does not show what Arius argued that Paul regarded Christ as a creature like “all creation (pases ktiseos…). It is rather the comparative (superlative) force of protos that is used… Paul is here refuting the Gnostics who pictured Christ as one of the aeons by placing Him before “all creation” (angels and men)… Paul takes both words to help express the deity of Jesus Christ in his relation to the Father as eikon (Image) and to the universe as prototokos (First-born).”
In Romans 8:29, the Lord Christ is described as “the first-born among many brethren.” These brethren are, of course, the glorified Christians. Here the Lord’s superiority and sovereignty over “the brethren” is acknowledged, as well as His leadership in their salvation. “As the brethren of Christ, all Christians will share his destiny (c.f. Heb. 2:10-17), and Christ is the pre-eminent Son among the sons of God (c.f. 1:3).” In Hebrews 1:6 we read, “And when He again brings the first-born into the world, He says, “And let all the angels of God worship Him.” Here the idea of pre-eminence is obvious, as all of God’s angels are instructed to worship Him, a privilege rightly reserved only for God (Luke 4:8). The term prototokos is used here as a title, and no idea of birth or origin is seen.
I think the point is simple. Indeed, the fact that the Greek word for created (Protoktisis or Protoktistos) is nowhere to be found in the New Testament with regard to Christ Jesus, the Son of God, speaks volumes. It’s not there because the Son of God, who is the Word or Logos, was himself never created. Yes, he was born of a woman and dwelt with us, but prior to giving up the glory he shared throughout eternity with God the Father, he was the eternal, the uncreated Son of God through whom ALL THINGS were created. He is the creator, not the created.
Edit: Just because someone has cited a non-biblical use of the word 200 years after Paul does not prove that the word only existed then!