The Churches that are now Orthodox have continuous lineal succession from the Apostles.
So does the Church that is now Roman Catholic.
Each can say that the other 'split off' from itself, and there is no 'objectively right' answer that can be determined without taking a side in the Schism. If the Orthodox Church's claim that the Roman Catholic Church added to the Faith and is heretical is correct, then the Roman Catholic Church can reasonably be said to be newer, having come into being when the Church of Rome abandoned Orthodoxy.
On the other hand, if the Roman Catholic Church's claim that the Eastern bishops wrongly rejected (among other things) the authority of the Roman Pontiff and thus split from the Church and are schismatic is correct, then it can reasonably be said that the Orthodox Church is newer, having come into being when the Eastern bishops abandoned Catholicism.
To ask 'Which Church is older?' as if it were independent of the question of which Church is true is meaningless.