From the Orthodox Outlet for Dogmatic Enquiries.
There are thousands of patristic references to Adam – an immeasurable chaos. However, it will be hard to locate a verse that refers to Adam in an absolutely univocal manner; i.e., a verse that cannot but imply a specific person.
An endeavor like this is a difficult one, for two reasons:
a) Because the Fathers had no cause to outrightly state (per our rationale) that Adam “is not a symbolic person”. Such an issue had not been put forward as a theory during their time, which is why they did not preoccupy themselves with something that they regarded a given fact; and
b) Because in the case of Adam, a multitude of symbolisms do also apply, however without them annulling his literal existence as a person – as the hypostatic beginning of mankind.
It is for this reason that in the present article priority has been given (among the multitude of texts that could have been cited), to the more palpable ones, without the need for one to have a knowledge of classical Greek – such basic and essential texts being: the Holy Bible – the Sacred Canons – two or three of the major Fathers and a very concise analysis of the ‘person-centred’ theology, so that anyone can comprehend just how significant the literal acceptance of the person of Adam is, for the Christian faith.
To answer this question we could begin with the New Testament itself.
In the Gospel of Luke which presents the genealogy of Jesus Christ (Luke 3:23-28) – in other words, the persons through which human nature  “reached” the Lord – it is apparent that Adam is mentioned as one of many other historical – and not symbolic – persons:
“…of Cainan, who was of Arphaxad, who was of Sem, who was of Noah, who was of Lamech, who was of Methuselah, who was of Enoch, who was of Jared, who was of Maleleel, who was of Cainan, who was of Enos, who was of Seth, who was of Adam, who was of God.” (Luke 3:36-38)
Thus, the Orthodox Church has accordingly instituted the Feast of the Holy Forefathers,  during which the following resurrectional (“sticheron”) hymn is chanted, where it again is impossible to arbitrarily exempt Adam (as if he were only a symbolic character) amid an entire sequence of historical persons:
“Come, all you lovers of feasts, let us laud with psalms: Adam the Forefather, Enoch. Noah, Melchizedek, Abraham, Isaac and Jacob; after the law Moses and Aaron, Joshua, Samuel and David; after whom Isaiah, Jeremiah, Ezekiel and Daniel and the Twelve, together with Elijah, Elissaios and them all; Zechariah and the Baptist and all those who proclaimed Christ, the life and the resurrection of our kind.”
In the Sacred Canons of the Church, Adam is commemorated in one of the Canons that were issued by the Synod of Carthage (AD 419). Of course this was a Local Synod, however its Canons acquired ecumenical authority after having been validated by the 2nd Canon of the Quinisext Ecumenical Synod. The 109th Canon of the Synod of Carthage mentions the following about Adam – whom it obviously treats as a historical person with a body and a soul:
“…Whosoever says that Adam, the first-made man, was made thus mortal, so that whether he sinned or not, he would have died in body – that is, he would have exited the body as a soul, not on account of sin, but by natural necessity, let him be anathema.” 
Adam’s historicity is equally stressed by the prominent Father of the Church and recapitulating dogmatologist, Saint John of Damascus:
“… everything that the Father has are also His (the Holy Spirit’s) except for unbegottenness; which does not signify a difference in the Essence or the status, but the manner of Their existence – just as Adam was unborn (for he was a creation of God) and Seth who was born (for he was a son of Adam) and Eve, who proceeded from Adam’s side (for she was not born), thus they too do not differ from each other in nature (for they are all human beings), but only in their manner of existence” .
Saint Athanasius the Great regards Adam not as a symbolic figure, but as much a historical one as Moses; and this is also confirmed by the fact that he speaks of the Incarnation – the Lord’s “entry” into human history:
“…and, albeit immediately able, even from the very beginning in Adam’s time, or Noah’s or Moses’, to send forth His Logos, He did not send Him… 
Moreover, we can also discern the same correlation (about the historicity of Adam’s person) in the words of the Apostle Paul:
“… but death reigned, from Adam up to Moses…” (Romans 5:14)
But even in regard to the content of Orthodox Theology, it is an entirely inappropriate perception that would give priority to the “essence” over the true being, the “person”.
In order to clarify these terms with certain examples: “lumber” is an essence, but “wooden objects” are the beings. Respectively, “humanity” is understood as being the essence, but “the human” is the being, the person. The being is something tangible and we perceive it with our senses, whereas we only have indirect communication with the essence.
In the “person-centredness of Hellenic Patristic thought [...] first place is no longer given to the notion of the essence, but to the person, the existence, the being. Instead of an impersonal ‘divine’, reference is made to a personal ‘God’, Who is not perceived as the supreme ‘being’, but as the sublime ‘o wn’ (He Who Is), the way He revealed Himself to Moses” .
As Saint Gregory Palamas expresses with clarity:
“…when God was responding to Moses, He did not say ‘I am the essence’, but ‘I am the One Who Is’ (o wn); for, (the name) ‘The One Who Is’ does not imply that ‘He Is’ from the essence; rather, it is the essence that comes from the being; because He, the ‘One Who Is’ has included in Himself all of being” 
This helps us to understand that the Fathers refer to Adam as a “being”, as a “person”, and not as an “essence”, not as the symbol of “mankind” – a stance that would not have been consistent with the overall viewpoint of their theology.
 “Christ bore Adam’s nature, without however being ‘of Adam’. He was not part of the natural continuity of descent of all humans, from a natural (biological) forefather. While he did have Mary as His mother, an actual descendant of Adam (and this guarantees the authenticity of His human nature), He did not have a natural (biological) father; a fact that exempts Him from any incorporation in the natural roots of the race that Adam represents as a patriarch”. (Andreas Theodorou, “Basic Dogmatic Teaching – Answers to questions on Dogma”, 3rd edition, Apostoliki Diakonia, Athens 2006, p. 83).
 “Adam and Eve (December, Sunday of the Holy Forefathers). The commemoration of the first-created is observed together with the remaining forefathers of Christ, on the Sunday before Christmas, at times on December the 16th, at times on the 18th and at other times on the 19th of the month” (Sophronius Eustratiades (Metropolitan of Leontopolis), “Calendar of Saints of the Orthodox Church”, Apostoliki Diakonia, Athens 1935, p.10)
 Panagiotis I. Boumis, “Canonical Law”, 3rd ed. augmented, Gregoris, Athens 2002, pp. 39.41
 Original and translation taken from: Prodromos I. Akanthopoulos, “Codex of Holy Canons”, 3rd ed., Vanias, Thessalonica 2006, pp. 340. 341
 Original and translation taken from: St. John of Damascus, “Exact publication of the Orthodox faith” (transl. N. Matsoukas). Pournaras, Thessalonica 1992, pp. 54-57.
 St. Athanasius the Great, “Complete Works”, Dogmatics 1 (Against Arians 1), by Patristic Editions Gregory Palamas, Thessalonica 1974, pp. 112-113.
 Marios Begzos, “The Future of the Past – Critical introduction to the Theology of Orthodoxy”, Armos, Athens 1993, pp. 41-42
 St. Gregory Palamas, “A catalogue of the outcomes of the incongruous”, No. 37, found in: Writings, tome 1, ed. P. Christou, Thessalonica 1962, p. 666