If there is a girl who is 14 and she had sex with a male who is 23, is that statutory rape? Once she turns 16, and they still have sex, would that still be statutory rape?
How long could the guy go to jail?

Yes, this is statutory rape. He could still be charged with statutory rape even after she turns 18 if she files charges. Jail time depends on many factors and is ultimately up to the judge. The law is below.

§ 14‑27.7A. Statutory rape or sexual offense of person who is 13, 14, or 15 years old.

(a) A defendant is guilty of a Class B1 felony if the defendant engages in vaginal intercourse or a sexual act with another person who is 13, 14, or 15 years old and the defendant is at least six years older than the person, except when the defendant is lawfully married to the person.

(b) A defendant is guilty of a Class C felony if the defendant engages in vaginal intercourse or a sexual act with another person who is 13, 14, or 15 years old and the defendant is more than four but less than six years older than the person, except when the defendant is lawfully married to the person. (1995, c. 281, s. 1.)

Sentences can range from 0-339 months depending on several factors.