I think it's pretty reasonable that the earth is no older than 15000 years old.
While anyone can quote bible verses, I try to hit at the "scientific" fallacies, which cause people not to believe any biblical arguments anyway ~_o
The origin of life is IMPOSSIBLE. Not just very very very very very unlikely. There are certain chemical reactions found IN life and ONLY in life that cannot occur naturally anywhere else, under any circumstances. Also, in the rare case that some of these reactions occurred, the chances of all of the pieces coming together in ANY "compatible" order is insane.
Also, evolution does NOT explain life. I think it is a very good mechanism for survival, and allows species to adapt to long-term environmental changed (*coughglobalwarmingcough*). However, there is ZERO proof for any changes in species, and an evolutionary change in chromosomes (e.g. We have 46, monkeys have like 44) has no explanation.
And if life hasn't evolved over millions and millions of years, then it definitely MUST have been made by a creator. And if it's been made by a creator, then I find it perfectly believable that the earth is only 10-15k years old ^_^