My kids are 14 and 8. The rule is simple no phone/devices in your room after 10pm - yes the 14 year old whined and protested when we implemented this rule last year. Now it's just the norm (kids adapt) and she puts her phone on the charger in our bedroom every night.

I don't expect this rule to change regardless of their age. In our house being 18 doesn't mean anything - our house, our rules.