Rather “an old man does not change his opinion easily”
#2 is ok.
Homo sapiens non semper sapientissime agit. Wise man never repel the wisest.
Yes, agere has many meanings, but here it is safer to understand it as “act, behave”, and non semper means rather “not always” than “never” (numquam), so : “Wise man does not always behave in the wisest way.”