NEVER put them on sand. Leopard Geckos will get impacted at any age.

Here is a picture of a bearded dragon next to the sand that he was impacted with, that is the same sand they got out of him. http://www.repticzone.net/images/7600/sand.jpg

here is a picture of real impaction, this picture is of the intestines after your gecko gets impacted. http://repticzone.com/cgi-bin/photos...owel%20being%2

Please don't put your gecko on sand. Keeep them on repti-carpet, paper towels, or tiles their whole lives.