According to naturalism, the earth and universe are several billion years old. However, the methods used to arrive at these long ages (including radioisotopes and erosion and deposition rates) are based on many assumptions. When these assumptions are taken into consideration, the results of the dating methods yield ages far more consistent with a biblical timeframe. Remember, you’re not denying operational science when you deny the millions-of-years idea; you’re denying a naturalistic interpretation of the past.
To find out more about the problems with the various dating methods, visit www.answersingenesis.org/go/young and www.answersingenesis.org/go/dating.
Additionally, the idea of a millions-of-years old earth is a relatively recent invention. Until the late nineteenth century, few people believed the earth to be so old. Several scriptural geologists challenged those who held to an ancient earth. For more information, see www.answersingenesis.org/go/scriptural-geologists.