Cons: The other couple may not share the same values as your Christian teen.
The Solution: Try using that age as a "review" age.
While all of these rules are appropriate, it will be easier for your teen to follow your rules if they understand where the rules come from.
Don't just cite Scripture -- explain how it applies.
Cons: Demanding that your child wait until marriage to have sex without explaining why may backfire.
Using a punishment approach (the infamous, "If you have sex, you will go to Hell" approach) may only make your teen more curious.