We never use sand at any age. I have seen too many customers with dead dragons (both adults and babies) impacted on sand that promises to be safe. My advice, like many, is to stick with reptile carpet, tile, or paper.
If you insist on using sand, use playsand, wait until the dragon is a year old, and feed them in a seperate enclosure. Change it often because it is just a giant litterbox harboring parasites. It gets very smelly quickly. It is more of a hassel than it is worth so I cannot stress how much you really should not use it or any loose particle substrate. :wink: