The earliest Christians were Jewish and they had no tradition of human forms in their religion. That changed when other peoples adopted Christ.
When Greeks (or Greek influenced peoples in the Near East) became Christianized, they adopted the human forms that made most sense to them; Jesus as the young shepherd, and the older bearded mature man (who was a teacher).
>>The earliest Christians were Jewish and they had no tradition of human forms in their religion. That changed when other peoples adopted Christ.
But they had Jesus, the actual man, and they believed that he was also God. So, when those “other peoples” joined and asked “what did he look like?”, the early Jewish Christians could describe him based on second- or even first-hand knowledge.
Recently a synagogue was excavated in Syria (from BC era) that had biblical scenes with human and angelic figures painted on its walls. So at least some Jews did depict humans at their place of worship.
Ancient Church Tradition says that St Luke "wrote" the first icons as a means of instruction and a refutation of the heresy that Christ was not really a man (as well as fully God).
I submit this is the human form that makes the most sense. Who hath believed our report? and to whom is the arm of the LORD revealed? For he shall grow up before him as a tender plant, and as a root out of a dry ground: he hath no form nor comeliness; and when we shall see him, there is no beauty that we should desire him.
Isaiah, Catholic chapter fifty three, Protestant verses one to two,
as authorized, but not authored, by King James