When to have one.

old enough, starting at 18 'AND' emotionally stable 'AND' spiritually stable 'AND' financially stable

your question can be answered in different way. you may need to be little bit more descriptive on your asking. well, there are few aspect we need to consider before having a kid. 1. you should be at right age before you have kid as per doctor's rule. 2. you both should be mentally ready to have a kid 3. you may sometimes need a family support before you decide for having kid. 4. you have to financially capable to have a kid. 5. you need to love kid and need to have a great affection before having kid. 6. you have to get little vacation from your career or profession. - if all these things are ok with you, i guess that will be the best time to have a beautiful kid in your life.

When you are ready mentally. A lot of people say that the financial aspect of having a child is important and that is what most people base things on. I think that mental readiness is the most important to be able to give that child the best life. If you are not mentally and emotionally ready, you nor the child will have the best result from this.