Staying up late

Last night, I put Lon to bed, gave him a kiss and left him to sleep. A little while later we hear a huge THUMP! I ran upstairs to see if he fell out of bed.  It was not him, it was his book and flash light. He was trying to read with the flash light in bed!   I say trying since he is still sounding out most words.   I wonder what age I started doing that? I still read in bed with a flash light. Just when you are a grownup they call them book lights