Somewhere I saw a chart of tree sizes compared to their probable age, classified by species. Actually, there were a few, but most were clearly written by someone with his head in his back door if you know what I mean.

Does anyone know of one that is acceptably accurate at least?

Nope. Too many variables affect growth rates of trees. Density of the forest stand, soil type, soil moisture, which side of a mountain where it is found.

This would be my thought too.

Plus the possibility that the tree was under a canopy for a while instead of gathering proper sun could affect its size versus age

I agree. Soil nutrients, wet years, dry years, sun exposure in a particular spot, pest pressure, so many variables influence the growth of a tree. You could have one tree grow 3’ one year, and 20 feet away the same species tree might only grow 6” for whatever reason

I planted a bunch of black walnut seedlings (hundreds) on the same site, on the same day thirty some years ago.

Now I have to harvest them. The mean dia is about 14", but range from 10-20.

Yip, too many variables, to get more than "order of magnitude" accuracy.

Because of the factors others here have stated, Tree size is a poor indicator of age.

what they all said.

having said that, here in the eastern US, tree HEIGHT (species specific) at a given age, is a good indicator of site index, or quality.

Site index charts for specific soil types are printed for certain species of trees. They give a pretty close indicator of how good the soil is by tree height at certain age