Almost all my adults have reached level 8 before they died. I think that they work better, with less distractions, when the game is off, so I make sure I give them the green glove or a treat for working each time I switch the game on. I never keep the game open for long and close it using App Manager each time, not just by the back button; that way it's no longer running in the background.
The wife is generally slower than her husband because she has to take time out to carry babies around, but with judicious application of the glove, plus fruit or candies, she has made it to master eventually; in some cases she's beaten her husband, even with that considerable handicap.
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To err is human; to arr is pirate.