I have been looking for this for a long time. I finally just Googled it…
“Right-click the selection you want to have the date picker show up for (i.e. single cell, entire row, entire column) and then open data validation. Set criteria to A valid date and click Save. Now just double-click the cell!” Here it is!
2. Double-click the cell and up pops the date picker!
“Anyone else ever have a ton of work to do, so you just check your Gmail before you get started and end up clicking on your Google Calendar and then think you’ll just click settings and you scroll to the bottom and see you can actually change the background image on your calendar and then end up spending most of the morning trying to pick the perfect background image that will look good in both your monthly view and 5-Day view? I know, right.”