Not always. For most girls, I would say 18 is too young but that's not true of everyone.
Babies are not fun. They are nothing but work, work and more work. Yes they are sweet and cuddly but they are also a big responsibility.
Do you have a steady committed relationship? It helps to have two people working together.
If that relationship falls apart, can you do it on your own?
Do you have a good job and a place of your own? If you can't afford a studio apartment, you can't afford a baby.
Do you have good health insurance? Babies get sick.
How will you handle daycare when you work or go to school?
Will you feel left out if your friends are out on a Saturday night and you are home because you can't find a sitter or can't spare the money for partying?
And if the birth doesn't go perfectly, are you prepared for a less than perfect baby? One that needs special help or constant care?
Are you emotionally ready for the late nights, the emotional strain, the lack of sleep the first year gives you?
Do you have a support system to give you the break you'll need?
If you have a drug, alcohol problem, are you willing to fix that first before having a baby?
There is no right answer for everyone, this is something you have to decide on your own. At 18, you should be out of high school and are a legal adult. Make up your own mind. Under 18, you are not a legal adult so don't.
And think about what the baby needs, it's more than love. Can you provide it?