When does a person go from kid to adult for doing one adult act but not the other?

Just when is a kid and adult? Let say for instance there was a girl, we will call “Lana”, and a guy we will call “Jake” who were in love with each other so they believe. Lana was 14 and in the 8th grade when she meets up with Jake the son of her parent’s friend, he was a junior. She was raised as an only child by very intelligent, studious, no messing around parents. Most of her childhood was spent around college educated adults so she was quite mature and versed for her age, he (Jake) was kind of a slacker ne’er do well, more into guitar than books. She liked his semi bad boy style, he her prim “Ms Poindexter” mannerisms. All is fine they date but no sex, somewhere after her 15th birthday sex comes into the picture (He is still under 18). When she is 16 (which make him now 19) there is a pregnancy scare but it is a false positive.

The gig is up, her parents are mad, feels Jake corrupted their little girl, file charges etc. Jake goes to jail, needless to say, the union is a bust. She is moody for weeks then she manages to get her mom’s “for protection only” 9mm and runs off with a girlfriend, they go on a 3 week crime spree (you still have to eat while running away) where they robbed 2 liquor stores, and one quickie mart, in the process one of the clerks is shot loses sight in one eye. Naturally they get caught. Because she is 16 and her partner on the run is just over 17 the DA goes after them as adults.

If she was too stupid to fully understand sex to consent to it with a young man she has had a 2+ year relationship with how do she all of a sudden fully understand the consequences of her action? Do crime makes you more adult even though nothing has changed with the person physically or mentally from before? Is the law being slid on a scale not uniformly but to better benefit the state or the law? I think the spirit of the law should be if you call a kid a kid, then they are a kid until they are 18, no matter what. When you play football a holding call is marked off the required distance whether the player committing it is a popular well known super star or a bench warmer in the game to spell a starter, there is no sliding scale depending on how the ref wants to call it and against who. Wouldn’t people respect the law if the law was totally level?