Victor Stone’s powers activated during his teens, with a little help from Starfire, who in this Earth seems to have some sort of telepathic powers. Notice how the metal on Victor’s body seems to be liquid?
Later on we learn that Victor’s mother, Elinore Stone, used him and the other Teen Titans as test subjects. Since most of their other subjects kept dying and rejecting the power grafts, Starlabs decided to use orphan babies so that their powers would grow with them. Victor, whom they codenamed Cyborg, was grafted with the living metal from Starfire’s ship.
From – Teen Titans – Earth 1 Vol. 1