Disclaimer: This method uses commands, so create a copy of your world and use it there, or else you will no longer receive achievements in your world.
time query command can be used to check the in-game days that have passed since you created your world. You can also check the number of ticks that have passed since you created your world.
/time query day
Shows the number of in-game days since you created your world. (Each day lasts 20 minutes, 10 minutes of day, 10 of night.)
/time query gametime
Shows the number of ticks since you created your world. (One tick is 1/20 of a second.)
How to create a copy of a world:
- Open the setting for your world by pressing the "pencil" button. (You need to leave first)
- Click on the Game settings tab.
- Scroll down to the bottom, and click on the Copy World option.
- You should now see the copy of your world in the worlds menu, named: "Copy of
Name of your world"