I know what you mean! My two cats were both adults when I got them, as was one dog. When I got the second dog I was looking for a young adult, but ended up with a puppy. One of our horses was an adult when we got him (BIG difference in horses in terms of the amount of training the babies need), and one of our goats was an adult when we got her. Many times I like getting an adult so I'm that much closer to where I'm going with that animal (horses: able to ride, goats: able to breed and get milk). With cats and dogs, I like not having to deal with the baby stages... To each their own!
I like my baby snakes, but there's something about a sub-adult or adult that I really like too. So far, in my limited experience, they've just been calmer and easier to deal with.