When did the off-shoot protestant sekts decide that catholicism cease to be christian?

Catholicism exist since 313 a.C. It's the most ancient christian denomination in existence. But it's not about age. If who is right is who is the oldest, so bye jews, buy christians. Induism is right. You have to obey the gospel of Christ and man, catholicism NEVER did it. Just read the bible and compare it with catholicism history.