Veilds are easy to care for if you learn the proper housing and care. As with nost things the things you need to house and care for a veild (or any animal) will greatly exceed the small amount of the actual animal. Your main cooncerns will be feeding,watering, and lighting. Once you get those 3 things understood you will not have problems. \
As for age get one that is at least 3 months old (if your a beginner) as they are hardier and past the delicate and natural selection stage (when they just die of no apparent cause).
There's a good book by Gary Ferguson and Philippe de Vosjoli called "Care abnd Breeding of Chameleons.