For your first bearded dragon, I would recommend buying an adult (at least 2 years old). Adopt one from a local reptile rescue, animal shelter, or off your local classifieds if you can — this is where you are most likely to find an adult beardie looking for a new home. They may not be as small and "cute" as the babies, but adults are more durable and more likely to tolerate common beginner mistakes.
Bearded dragons make great first-time reptiles — but be warned, their care requires a substantial initial investment. Because you have to mimic their native habitat in your own home, a lot of special equipment is needed. But don't let that scare you away. If you want a beardie companion, with a little determination you can make it work.
Adults are great for first time beardie owners because 1. They’re more easygoing/docile than their skittish baby counterparts and 2. They eat far fewer insects than babies, since greens and veggies are the emphasis of an adult beardie’s diet. The staggering amount of insects a baby can eat in a 24-hour period can be daunting to a first time reptile owner. My friend recently adopted an adult beardie from a reptile rescue and it’s one of the sweetest, most personable lizards I’ve ever encountered. I highly recommend going this route.
I think I personally made the right choice with adopting a 6-month old Dragon but that said, I am home all day and have PLENTY of time to take care of his juvenile needs which are extensive, to say the least. I don't have any experience with adult Beardies yet but I'm more inclined to agree with what the posters above are saying.