I'd go with the older dragon as well but good points have been made about possible need for some extra vet treatment so keep that in mind and budget. I only adopt dragons who are in desperate need of a good home and while it can be more costly and time consuming, it's very rewarding. They are quite likely to bond with you although it may take some more time than usual. 6mo is still a very young dragon, not even fully grown yet, so you're still getting in near the beginning of their life.