Many researches reported the difference of crystallinity of various types of cellulose. The more age of tree the higher cystallinity of cellulose. However, is there a rule of this effect?
Biomass properties (in trees specifically) improve from pith to bark. The lignin content and the hemicelluloses content decrease from pith to bark. The density of the tree increases from pith to bark except for ring porous hardwoods. The length of the cells also increase from pith to bak. So if the "old age" of a tree is associated with positive attributes, perhaps it is plausible to suggest that cellulose crystallinity should also improve with the age of the tree.