The difference between a modern day board and one pulled from old barn

The main difference between the two boards is the age of the tree when it was cut. The older board has over 80 growth rings and neither edge of the board is near the pith, where the rings would look more like the board on the right. There is no sapwood showing (lighter in color) so the board was not near the bark. The tree must have been at least 100 years old, possibly much older. Because the grain orientation is near vertical the board would remain relatively flat even when it absorbed moisture or dried out.

The newer board shows sapwood at the corners on the right side. The age of the tree could have been as low as 20 years when it was cut, although tree farms are harvested on a longer schedule. Maybe this tree was cut during thinning. The board is slightly cupped because it has dried some since it was milled. If it were to be used as a deck board and became much wetter it would cup in the opposite direction.

The lower quality wood still works OK for framing and building codes factor in the quality of lumber typically available. Structural lumber is also graded to insure it will be strong enough.

I recently saved some 1 x 10" vertical grain Douglas fir trim boards that were installed in 1977 and they look almost as good as your old barn board. The new trim isn't nearly as hard or as old but it still works fine as painted window trim.

The difference between the boards is not only age as Steve points out, but the conditions in which they grew. A forest tree with competition will grow much slower with tighter growth rings than a more open grown or plantation trees. In old growth forests, tree rings can be much tighter than your old board. Also weather, droughts, wet spells, cold eras and warm eras cause variations in ring width. Scientists use a technique called dendrochronology to determine the age of timber through time. They core sample a tree or logs and compare growth ring patterns over time. they have developed a history of core samples and in some cases can determine when a tree was harvested a thousand or two years ago. It's pretty fascinating stuff. I have a section of heart wood from an oak post that I excavated on an archaeological site that has growth rings several times more dense than your sample. Some day I may get it carbon dated, which is another tool that helped create the dendro history. If you ask ChatGPT, you'll probably get a more accurate answer than I have stated.

That's your basic quarter-saw and flat-sawn examples.