TF, when, exactly, do you believe Roman Catholicism began?I answer:
If Roman Catholicism is defined by her (supposedly) infallibly defined dogmas, her birthday is November 1, 1950, which is when her pope defined the fiction of the bodily assumption. If she is defined by the last (supposedly) ecumenical council she accepts, she's even younger (December 8, 1965), the date of conclusion of the Second Vatican Council. If she is defined by her canon laws, the most recent major edition was January 28, 1983. If she's defined by her current pope, then she's newborn.
But if she's simply vaguely defined as a movement, it's hard to provide a fixed date. Benedict XVI treated Thomas Aquinas (d. 1274) as the father of Roman Catholicism - despite the fact that Thomas Aquinas' views would place him outside the RCC today.
Perhaps better dates would be the dates of the councils of Constance (1418), Florence (1445) and Trent (1563), where certain strands of scholastic theology gained ecclesiastical dominance over other strands. Then again, a lot of Tridentine RCism has been undermined in contemporary RCism.
And frankly, that's probably the best way to date the movement - to the "late medieval" period - 15th or 16th century, although there were undoubtedly doctrinal roots that go back earlier, even while recognizing that RCism continues to change even today.
That doesn't mean that no one before 1054 held to any views in common with Roman Catholics, and it doesn't mean that things like the Edict of Milan or the forged "Donation of Constantine" were insignificant factors in producing what eventually came to be RCism. Still, calling anyone in the late patristic or early medieval period "Roman Catholic" is anachronistic.