Those are all boring and unimaginative questions u picked. How about "what decision did u make that u would like to change the most?" Or "what stock should invest in to become wealthy"? Or "who should I warn that they have a life-threatening illness?"
If u ask them the biggest mistake u made they won't tell u cause then u would ruin ur future self instead of asking questions make sure u let them know u won't change a thing about them in the present.