Thanks to Steel!

Warp is the master of time--able to go back and forth at will, he goes into the Titans past to steal the Clock of Eternity--"valuable in the past, priceless in the future." History says that the clock was stolen in the past, by him, so he fulfilled the History and went back to steal it--but the Titans interfered, with Starfire going forward in time with Warp by 20 years.

In the end, Starfire was able to return the Clock of Eternity to their past--but not without disrupting Warp at the same time. His vortex modulator was tampered with and he was turned back into a younger--much younger--form of himself: when he was a baby.