There is no age at which sand is a good idea. It will always harbor bacteria, pose an impaction risk, etc. I predict this thread will explode in 3...2...
I'm a new beardie owner too, i have a 6 month old beardie who i keep on sand but when i feed him, i feed him on his log, basking rock or in the plastic container i keep my food in. Does that reduce the risks of keeping him on sand or should i not use sand either?
It's generally recommended that you don't use sand at any age, at any time, ever. Have you noticed how they go around licking everything? That's kind of how they feel their way around the area, and they can end up ingesting a lot of sand just like that - which is likely to cause impaction. Everyone always mentions impaction when warning against sand, but really I think the worst part about it is that it's soooo unsanitary. It's like living in a giant litter box... would you want to live in a litter box? No, that's disgusting lol! It's just nearly impossible to keep it clean. You may be scooping up the solid poop but all the fluid traces that get missed will most likely end up right back in your beardie either by them ingesting it or pretty much marinating in it. Pretty nasty if you ask me
I've also heard of it getting in their eyes, just one grain, and causing infections and the like, but that's not as common. No matter what you do, the beardie is gonna eat sand, and enough grains over enough time risk an impaction in their intestines. There are people who've used sand and gotten away with it, but it's like smoking- maybe you won't die of cancer, but why roll the dice?
Another to say it is never okay to use sand. I used to use it when I didn't know any better. Use ceramic tile instead. (Paper towels and newspaper are also acceptable).