Eastern Kingsnake - change of behavior and several other questions

Question
Hello! Thank you for reading my (unfortunately, long) message. I have recently bought a beautiful female Eastern Kingsnake, about 8 months old. (Question nr. 1) Is she still considered a baby snake at this age? How will her  age affect my experience with her? I am her 4th owner so far, she has quite a long history behind her already. Should I expect her to be more hostile, because she didn't had the opportunity to "attach" - I know snakes don't really get attached - herself to one single owner? (Question nr.2) And speaking of hostile...when I brought her home (less than a week ago) and placed her in her new vivarium she proved to be VERY docile. I picked her up right after that and continued to do so in the following days. She was very relaxed, walked on my hands, sometimes even didn't want to climb down to the branches in her vivarium. She would just stand still on my arms (without raising her head in a "get prepared to strike" position, or anything). Starting yesterday she suddenly changed her behavior. I can't pick her up anymore, she is constantly striking at my hand and rattling her tail. She is not even walking in her vivarium when I'm in the room. She just stands still, ready to strike, always watching me through the glass.
-I always shower/wash my hands before handling her, so the changing of the smell is not an issue...I think
-haven't fed her so far, I will try tonight, but it hasn't been long since she has been fed (less than a week)
-she doesn't show signs of shedding her skin
-the temperature in her vivarium is between 22-27 degrees Celsius
-she has several places to hide and her vivarium is large enough

If I haven't given all the details you need, please let me know. I will also use gloves starting from tonight. What do you think has caused this change in behavior and how should I act from now on?

Thank you. Have a good day!

Answer
First off, everything in your setup sounds fine...the temps, hiding spots, etc.

Snakes don't usually "attach" to a person like a dog or cat would. A kingsnake under one year old will typically exhibit behavior just as you are describing. Keep in mind that in the wild, snakes are the most vulnerable when they are young. Their natural instinct is to defend themselves when faced with a predator. In this case, the predator is you. They don't know what your intentions are, so they react defensively by rattling their tales and putting up an aggressive posture. The best suggestion that I can give you is to use the gloves to get the snake out of it's vivarium, then remove the gloves and handle the snake. Often the snake will turn off it's aggressive stance once it has been removed from it's cage. If not, it may bite you. Kingsnakes do have teeth, so it will make a couple of very small holes that will probably bleed, but it doesn't really hurt once you get used to it. If it does bite, don't put the snake back, just keep handling it. Otherwise the snake will learn that biting resulted in the snake being let go and it may continue to bite. By continuing to handle the snake even if it bites, it will (hopefully) learn that biting didn't work. Also remember that if you do get bit, put some Neosporin anti-bacteria on the area when you are done holding the snake.

It doesn't sound like food is the issue. However, an 8 month old snake should be eating hopper-sized mice or maybe even larger. Often times people will continue feeding their snake pinky mice, essentially underfeeding the snake. The mouse should leave a small but noticeable bulge in the snake's belly that remains for a day or two. Remember not to handle the snake until the bulge disappears.