You’re tall enough when you can reach the light-switch.
(I had to use this photo because it doesn’t only have a light-switch
but to the left in yellow is our growth chart.)
Advice taken from the nifty little booked entitled
by: Cynthia Copeland Lewis
alice w. gold 
… and when you can reach the light switch… you have the power at your fingertips. Not only can you turn things on and off… but you can spark reactions from Mom & Dad when they get tired of it.
ToOdLeS.