As previously said, babies can't be kept on sand because they are more likely to get it in their mouth ( their aim isn't as good when catching prey) and its very hard for the to digest- leading to whats known as impaction. Adults may also suffer from this, however they are not at risk as much as babies.
Calci-sand is even worse!! This can harden up in their intestines when digested, as it forms a cement like susbtance when combined with moisture, and leads to impaction much more often than normal sand.
Personally I think slate tile in a vivarium looks awsome, and it keeps their nales nice and trimmed. It also warms up nicely under the heat, storing the heat through the night, and is much easier to clean and maintain.
I'm getting a baby beardie next week, I chose a baby because I would like to bond with it as early as I can, and have it in my life for longer. However there are many adult beardies and subadult beardies out there that need rescuing. It's really up to u in the end. Adult beardies need as much care and attention as babies- their temp and lighting needs are practically the same. Only difference is the babies eat more of smaller things, but most companies give you value for money e.g 500 micro size crickets for the same price as 25 extra large crickets.
I'm getting a 4ft x 2ft x 2ft tank for my baby, but sectioning off half of it with some thin wood, bringing the wood back as the beardie grows and needs more space. This saves money!