Answer:

I will assume you are talking about the Roman Catholic Church.  There is also the Eastern Orthodox Catholic Church and the Coptic Catholic Church.  These names are in a sense oxymorons, since the word catholic means universal.  By definition, there cannot be more than one universal church.

In any case, the Roman Catholic Church traces its beginning back to the original church which was established at Pentecost in AD 30.  Christians started the church in Rome almost certainly by AD 50.  Paul visited the well-established church in AD 63.  The Roman Catholic Church can trace its roots all the way back to the original Christian church in Rome.

This fact may be confusing to you, because you are probably aware that the Roman Catholic Church today is very far from holding to biblical Christianity, with its popes, vestments, sacraments, incense, celibate priests, nuns, church calendar and much more.  The Roman Catholic Church is clearly a very corrputed version of Christianity.  Nevertheless, it is a historical fact that the church in Rome can literally trace its roots in a more or less uninterrupted line to the time of the apostles.  Of course, Catholics, like Orthodox Christians, are very proud of their historical roots.  My suggestion is that you not argue with this claim because it is true.  The Episcopalian, Baptist, Methodist, Lutheran, Pentecostal and other denominations cannot claim what the Roman Church can claim historically.  Of course, genaeology does not equal truth and the fact that a particular group cannot trace its history back to Pentecost does not mean that they are not true Christians, but the facts of history are the facts of history.

Having said that, you should not be intimidated by the facts of history.  The facts of history show that gradually, over several hundred years, the early church, and especially the church in Rome added many man-made traditions to the simple truth of Christianity.  By the third century, they were baptizing babies and worshipping at the graves of "saints."  By the fifth century the Catholic Church accepted Original Sin and Transubstantiation.  Eventually, the Catholic Church invented false teachings and practices such as the Immaculate Conception of Mary, Purgatory, indulgences, celibate priests papal infallibility and the like.   Some of these are unbiblical traditions, others are false doctrines.   What you should do is try to find a church which is strongly committed to biblical Christianity and is willing to put biblical principles into practice.

John Oakes