Thank you for your kindness, your generosity, and your wisdom.
Can I say this in formal speech to an old guy who have taken good care of me and taught me a lot?
Is "wisdom" natural to use or is it overly formal. Is it just out of place?
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I think it is fine if this is what you appreciate in him. However, your question is a bit vague. You mention that you are looking for formal speech, but then you are worried you might be too formal. So I assume your relationship with the "old guy" is not highly formal.
I would formulate your sentence like this:
I am grateful (it is a bit more formal than just Thank you) for your kindness, generosity and wisdom.