Why not set up a new profile on your GOS phone and show them why it's not scary. Set it up with minimal privacy/security restrictions to make it the easiest transition. Any GOS setup is better than no GOS.
ALSO, Flip the question around. What do I have to hide is the wrong question. Instead ask, why do I need to share? It might be okay to share everything now, but when/if that changes, you can't go back and remove all you've already shared. If you keep everything secure/private now, you can always and easily change your mind later. Put yourself in a position that gives you OPTIONS in how to deal with unexpected future situations.
Perhaps ask about situations you know they regretted a decision they made. Perhaps posted something on social media by accident, sent a text to the wrong person, opened an email they wish they never clicked on, etc..
Also, ability to reduce battery drain through Bluetooth and wifi auto shutoff helps, right? And you can prevent apps from running in the background, which can be one of the biggest battery drains when you always have 42 apps you forgot about running in the background (I'm assuming this is the case, but I'm no expert).
Good luck!