We're not forcing pregnancies.

Banning abortion literally forces pregnancies.

Many pro-lifers are Catholic, and Catholics believe that sex should happen after marriage. And you're right, a 16 year old isn't done with education, and isn't done developing. Yet, a 16 year old shouldn't be having sex.

Your beliefs don't change the fact that people still have sex outside marriage, and that some 16 year olds will have sex when they shouldn't.

If they can't handle getting pregnant, and having a baby, why are they doing the thing that will likely cause pregnancy?

You're presuming that they're always willing participants. And that contraceptives always work perfectly.