The State Border Service warned that such information is fake. Restrictions on leaving during martial law apply to men aged 18-60. You can find out more about who can cross the border in the resolution of the CMU "On approval of the Rules for crossing the state border by citizens of Ukraine"
There is only Draft Law No. 9480, which proposes changes to the Civil Code, which provides for a ban on independent crossing of the border for teenagers, because currently all children from 16 to 18 years old do not need an escort or special permits to leave Ukraine.