That's funny because E B Elliot cites the very same Clement and this same story, as well as Eusebius's comments on it, as evidence of the late date of Revelation:
"Clement's support to a later date is found in story involving St. John after he returned from Patmos. The point being made that John was quite an old man when it occurred.
"Next Clement of Alexandria indirectly, but I think clearly, confirms the statement. In relating the well-known story of St. John and the robber, he speaks of it as acted out by the apostle on his return from exile in Patmos, 'after the death of the tyrant;' and represents him as at that time an infirm old man. Now 'the tyrant,' whose death is referred to, must necessarily be either Nero or Domitian; as these were, up to the end of the first century, the only imperial persecutors of the Christian body. And Nero it can scarcely be: since, at the time of Nero's persecution, St. John was by no means an infirm old man; being probably not much above, if indeed so much as, sixty years of age.
Thus it must rather have been the tyrant Domitian. So, in fact, Eusebius expressly explains Clement to mean. " (vol. I, p. 33-34)[Historicist.com]
Chapter 17. The Persecution under Domitian.
"Domitian, having shown great cruelty toward many, and having unjustly put to death no small number of well-born and notable men at Rome, and having without cause exiled and confiscated the property of a great many other illustrious men, finally became a successor of Nero in his hatred and enmity toward God. He was in fact the second that stirred up a persecution against us, although his father Vespasian had undertaken nothing prejudicial to us."
Chapter 18. The Apostle John and the Apocalypse.
"1. It is said that in this persecution the apostle and evangelist John, who was still alive, was condemned to dwell on the island of Patmos in consequence of his testimony to the divine word.
2. Irenæus, in the fifth book of his work Against Heresies, where he discusses the number of the name of Antichrist which is given in the so-called Apocalypse of John, speaks as follows concerning him: 3. "If it were necessary for his name to be proclaimed openly at the present time, it would have been declared by him who saw the revelation. For it was seen not long ago, but almost in our own generation, at the end of the reign of Domitian.
4. To such a degree, indeed, did the teaching of our faith flourish at that time that even those writers who were far from our religion did not hesitate to mention in their histories the persecution and the martyrdoms which took place during it. 5. And they, indeed, accurately indicated the time. For they recorded that in the fifteenth year of Domitian Flavia Domitilla, daughter of a sister of Flavius Clement, who at that time was one of the consuls of Rome, was exiled with many others to the island of Pontia in consequence of testimony borne to Christ.
Here is the story from Clement about the Apostle John with highlights by myself:
Having come to one of the cities not far off (the name of which some give), and having put the brethren to rest in other matters, at last, looking to the bishop appointed, and seeing a youth, powerful in body, comely in appearance, and ardent, said, "This (youth) I commit to you in all earnestness, in the presence of the Church, and with Christ as witness." And on his accepting and promising all, he gave the same injunction and testimony. And he set out for Ephesus. And the presbyter taking home the youth committed to him, reared, kept, cherished, and finally baptized him. After this he relaxed his stricter care and guardianship, under the idea that the seal of the Lord he had set on him was a complete protection to him. But on his obtaining premature freedom, some youths of his age, idle, dissolute, and adepts in evil courses, corrupt him. First they entice him by many costly entertainments; then afterwards by night issuing forth for highway robbery, they take him along with them. Then they dared to execute together something greater. And he by degrees got accustomed; and from greatness of nature, when he had gone aside from the right path, and like a hard-mouthed and powerful horse, had taken the bit between his teeth, rushed with all the more force down into the depths. And having entirely despaired of salvation in God, he no longer meditated what was insignificant, but having perpetrated some great exploit, now that he was once lost, he made up his mind to a like fate with the rest. Taking them and forming a band of robbers, he was the prompt captain of the bandits, the fiercest, the bloodiest, the cruelest.
Time passed, and some necessity having emerged, they send again for John. He, when he had settled the other matters on account of which he came, said, "Come now, O bishop, restore to us the deposit which I and the Saviour committed to you in the face of the Church over which you preside, as witness." The other was at first confounded, thinking that it was a false charge about money which he did not get; and he could neither believe the allegation regarding what he had not, nor disbelieve John. But when he said "I demand the young man, and the soul of the brother," the old man, groaning deeply, and bursting into tears, said, "He is dead." "How and what kind of death?" "He is dead," he said, "to God. For he turned wicked and abandoned, and at last a robber; and now he has taken possession of the mountain in front of the church, along with a band like him." Rending, therefore, his clothes, and striking his head with great lamentation, the apostle said, "It was a fine guard of a brother's soul I left! But let a horse be brought me, and let some one be my guide on the way." He rode away, just as he was, straight from the church. On coming to the place, he is arrested by the robbers' outpost; neither fleeing nor entreating, but crying, "It was for this I came. Lead me to your captain;" who meanwhile was waiting, all armed as he was. But when he recognized John as he advanced, he turned, ashamed, to flight. The other followed with all his might, forgetting his age, crying, "Why, my son, do you flee from me, your father, unarmed, old? Son, pity me. Fear not; you have still hope of life. I will give account to Christ for you. If need be, I will willingly endure your death, as the Lord did death for us. For you I will surrender my life. Stand, believe; Christ has sent me."
And he, when he heard, first stood, looking down; then threw down his arms, then trembled and wept bitterly. And on the old man approaching, he embraced him, speaking for himself with lamentations as he could, and baptized a second time with tears, concealing only his right hand.
Clements talks about John (after being released from Patmos), blessing a boy, who becomes involved in all sorts of nefarious activities over time. After some amount of time goes by, and John has wandered all around the country sides establishing churches and bishops, they call John back, who then hops a horse and rides across the countryside. Now given the account above, and realizing that there seems to be a substantial amount of time that has past, does the Apostle John’s actions sound like he’s 82 or 55 (realizing that he would be closer to 90)? Does it sound pausible that a 90 year old man (in those days) would hop a horse and ride hard to find a lost soul?
Given this story do you think Clements “represents him [sic: John] as at that time an infirm old man.” as Elliot claims. I don’t think so. Elliot obviously made up this statement to support his own contention. Too bad people didn’t have the Internet back then to check it out.