Simple solution do not talk about sex on the phone or internet. If there is a law like that it is to crack down on predators but I wouldn't take the chance even if it is my girlfriend.
AND no you can not have sex with her unless you check your state law and it is legal for a 23 year old to have sex with a 17 year old. Most states age of consent is 16 or 17 the law is but not with more than 4 years older so you need to find that out.
Will be right back with MD's age of consent.
### Edit:
Moral Outrage - Maryland - Age of Consent Laws
Age of consent is 16 BUT you could still have a not with anyone over 18 or over 20 law.