@gruber Answers do vary but their general consensus is 6000-12000 years, many leaning towards 6000. They rely on interpretations of biblical texts. Here are a few sources.
https://www.christianity.com/wiki/bible/what-is-young-earth-creationism.html (Use Kagi sunmarizer with this one as it will prompt you into cookie hell).
https://www.icr.org/article/six-biological-evidences-for-a-young-earth/
And then there’s this diatribe from Ken Ham https://x.com/aigkenham/status/1751576377072013461?s=46&t=eH8hnTmUjyw1xrwPlGxm-g