In this day and age, giving birth at 18 is too early.

...But do not worry too much.
Just 200 years ago, in my country (and in a lot of other places all over the world), it was normal for girls to marry and become mothers at 14 or 15.

A woman's body becomes ready for child delivery pretty early. At 15, almost all girls are fully developed for a child. The problem is in the mentality - at 15 most are still kids.
The past was different because kids were exposed to hardships a lot earlier in life. Many were working on the fields since 10 years old. These children would quickly become adults.

I believe that the most important question isn't "how old are you?", but "how ready are you?".

Do not fear hardship, as it makes you stronger.

// P.S. My sister also got pregnant early - at 19.
// . At 20 she got pregnant again.
// . That was 5 years ago.
// . Now she is working hard and studying in university.