Compilation of Jefferson on topic by "student of life" at Newsvine (my bold):

Every constitution, then, and every law, naturally expires at the end of nineteen years. If it be enforced longer, it is an act of force, and not of right. It may be said, that the succeeding generation exercising, in fact, the power of repeal, this leaves them as free as if the constitution or law had been expressly limited to nineteen years only. In the first place, this objection admits the right, in proposing an equivalent. But the power of repeal is not an equivalent. It might be, indeed, if every form of government were so perfectly contrived, that the will of the majority could always be obtained, fairly and without impediment. But this is true of no form. The people cannot assemble themselves; their representation is unequal and vicious. Various checks are opposed to every legislative proposition. Factions get possession of the public councils, bribery corrupts them, personal interests lead them astray from the general interests of their constituents; and other impediments arise, so as to prove to every practical man, that a law of limited duration is much more manageable than one which needs a repeal."

--Thomas Jefferson to James Madison, 1789. ME 7:459, Papers 15:396

Let us provide in our constitution for its revision at stated periods. What these periods should be nature herself indicates. By the European tables of mortality, of the adults living at any one moment of time, a majority will be dead in about nineteen years. At the end of that period, then, a new majority is come into place; or, in other words, a new generation. Each generation is as independent as the one preceding, as that was of all which had gone before. It has then, like them, a right to choose for itself the form of government it believes most promotive of its own happiness; consequently, to accommodate to the circumstances in which it finds itself that received from its predecessors; and it is for the peace and good of mankind that a solemn opportunity of doing this every nineteen or twenty years should be provided by the constitution, so that it may be handed on with periodical repairs from generation to generation to the end of time, if anything human can so long endure."

--Thomas Jefferson to Samuel Kercheval, 1816. ME 15:42

Forty years [after a] Constitution... was formed,... two-thirds of the adults then living are... dead. Have, then, the remaining third, even if they had the wish, the right to hold in obedience to their will and to laws heretofore made by them, the other two-thirds who with themselves compose the present mass of adults? If they have not, who has? The dead? But the dead have no rights. They are nothing, and nothing can not own something. Where there is no substance, there can be no accident [i.e., attribute]."

--Thomas Jefferson to Samuel Kercheval, 1816. (*) ME 15:42

The idea that institutions established for the use of the nation cannot be touched nor modified even to make them answer their end because of rights gratuitously supposed in those employed to manage them in trust for the public, may perhaps be a salutary provision against the abuses of a monarch but is most absurd against the nation itself. Yet our lawyers and priests generally inculcate this doctrine and suppose that preceding generations held the earth more freely than we do, had a right to impose laws on us unalterable by ourselves, and that we in like manner can make laws and impose burdens on future generations which they will have no right to alter; in fine, that the earth belongs to the dead and not the living."

--Thomas Jefferson to William Plumer, 1816. ME 15:46

A generation may bind itself as long as its majority continues in life; when that has disappeared, another majority is in place, holds all the rights and powers their predecessors once held and may change their laws and institutions to suit themselves. Nothing then is unchangeable but the inherent and unalienable rights of man."

--Thomas Jefferson to John Cartwright, 1824. ME 16:4

The generations of men may be considered as bodies or corporations. Each generation has the usufruct of the earth during the period of its continuance. When it ceases to exist, the usufruct passes on to the succeeding generation free and unencumbered and so on successively from one generation to another forever. We may consider each generation as a distinct nation, with a right, by the will of its majority, to bind themselves, but none to bind the succeeding generation, more than the inhabitants of another country."

--Thomas Jefferson to John Wayles Eppes, 1813. ME 13:270