One word for “someone who learns from others' mistakes"
Solution 1:
A wise person follows the "path through time immemorial" learning from others'mistakes.
Solution 2:
In simple English, A person who learns from other's mistakes may be called wise person
Solution 3:
I can think of the following:
fast learner or quick learner
sagacious
assimilator (as in one who absorbs new experiences)
Of course one would have to provide the context to fully establish the meaning. But I think that the situation described is too specific for a totally apt single word.
Solution 4:
Circumspect has the primary meaning cautious (bordering perhaps on over-cautious), but probably still connotes 'weighing up what's happening around oneself' - perhaps close enough to 'learning from others' mistakes'. There's no agent noun.