I QT mine for a minimum of 90 days at someone else's house. I prefer to buy younger animals, breeder-direct is ideal, as there's more potential for older animals to have been exposed to more collections, and thus more chance for them to pick up a disease along the way.
If I do get an older critter it's from someone who has had it for a while and who has a great reputation. If it's a proven breeder female and it produced a clutch during the last season, I give her a year off to recover, as I only breed my girls every other year anyway.