Yes, Christianity is older than Islam, if you consider the timing of the Prophet Muhammad. (570 Mecca - June 8, 632 Medina) The Qu'ran which is the book of divine guidance that came to him through Gabriel the archangel about 610AD. At that time the Qu'ran had been recited, every year till his last year when the Angel Gabriel asked him to recite it twice. The original Qu'ran is in Arabic.
In Christianity the first books (Gospels to be written) were in 65-70AD starting with Mark, then Matthew and Luke about AD and last John about 90AD. It is important to note it was not the apostles Mark, Matthew, Luke and John that wrote these gospels. The first Council of Nicea was in 325AD where they discussed Jesus as Son of God and the Trinity. The first books of the bible were chosen at this time. The two main collections were the Palestinian written in Ancient Hebrew and Aramic and the Alexandrian written in Ancient Greek. The original texts are unknown
However.. if you look the meaning of the word..and not as a Label.
Christian one who follows Christ. Muslim one who submits to the will of God. If you look at it this way. being a Muslim is older because the Prophet Abraham submitted to the will of God. So it depends on the term. But since you asked for religion and practice I would say Christian. I am no expert, just love studying it and learning. It is good to question and reason.