Hab 3:6 He stood, and shook the earth;
he looked, and made the nations tremble.
The ancient mountains crumbled
and the age-old hills collapsed.
His ways are eternal.
NIV

and

2 Peter 2:5 if he did not spare the ancient world when he brought the flood on its ungodly people, but protected Noah, a preacher of righteousness, and seven others;
NIV

The mountains and the world are "ancient" but not eternal (an attribute of God, not of the physical cosmos). I am persuaded from a variety of resources, Biblical and scientific, that the calendar age of the cosmos is in fact several thousand years, while the apparent age is much more since, like Adam, it began as a fully funtional (mature) system.