Why would God want to fool people with an appearance of age?
The earth looks old and mature because it is.
If you want to believe the earth is flat, or that the sun revolves around the earth, or that the earth is only 6000 years old, you are welcome to your opinion.
To broaden your mind a bit, try reading "Evolutionary Creation: A Christian approach to evolution" by Denis Lamoureux or "Chance or Purpose?" by Christoph von Schonborn. At least get the arguments for the other side.
I was raised as a Fundamentalist. I know all the arguments for a young earth. I can give them to you. But now that I am an adult, I find that there is a lot of information that I was not told that points to an old earth. Information based on fact and things that I can observe with my own eyes. Belief in an old earth does not shake my faith in God as Creator one bit, but makes me marvel at His creation even more.
Job 38:4 "Where were you when I laid the foundation of the earth? Tell me, if you have understanding.
Job 38:5 Who determined its measurements--surely you know! Or who stretched the line upon it?
Job 38:6 On what were its bases sunk, or who laid its cornerstone,
Job 38:7 when the morning stars sang together and all the sons of God shouted for joy?
Job 38:8 "Or who shut in the sea with doors when it burst out from the womb,
Job 38:9 when I made clouds its garment and thick darkness its swaddling band,
Job 38:10 and prescribed limits for it and set bars and doors,
Job 38:11 and said, 'Thus far shall you come, and no farther, and here shall your proud waves be stayed'?
Job 38:12 "Have you commanded the morning since your days began, and caused the dawn to know its place,
Job 38:13 that it might take hold of the skirts of the earth, and the wicked be shaken out of it?
Job 38:14 It is changed like clay under the seal, and its features stand out like a garment.
Job 38:15 From the wicked their light is withheld, and their uplifted arm is broken.
Job 38:16 "Have you entered into the springs of the sea, or walked in the recesses of the deep?
Job 38:17 Have the gates of death been revealed to you, or have you seen the gates of deep darkness?
Job 38:18 Have you comprehended the expanse of the earth? Declare, if you know all this.
Job 38:19 "Where is the way to the dwelling of light, and where is the place of darkness,
Job 38:20 that you may take it to its territory and that you may discern the paths to its home?
Job 38:21 You know, for you were born then, and the number of your days is great!
Job 38:22 "Have you entered the storehouses of the snow, or have you seen the storehouses of the hail,
Job 38:23 which I have reserved for the time of trouble, for the day of battle and war?
Job 38:24 What is the way to the place where the light is distributed, or where the east wind is scattered upon the earth?