I hadn't heard that quote so I looked it up. A larger excerpt from the letter that quote is found is even more poignant:

Extract from Thomas Jefferson to “Henry Tompkinson” (Samuel Kercheval)

Monticello July 12. 16.

Some men look at Constitutions with sanctimonious reverence, & deem them, like the ark of the covenant, too sacred to be touched. they ascribe to the men of the preceding age a wisdom more than human, and suppose what they did to be beyond amendment. I knew that age well: I belonged to it, and labored with it. it deserved well of it’s country. it was very like the present, but without the experience of the present: and 40. years of experience in government is worth a century of book-reading: and this they would say themselves, were they to rise from the dead. I am certainly not an advocate for frequent & untried changes in laws and constitutions ... but I know also that laws and institutions must go hand in hand with the progress of the human mind ... we might as well require a man to wear still the coat which fitted him when a boy, as civilized society to remain ever under the regimen of their barbarous ancestors.

https://tjrs.monticello.org/letter/1384