"I hope I'm ready"? :) Hope this won't lead to "I hope I do" at the altar.
You are either a family person or need to age enough for that:
What I refer to 'a family person' is:
Someone who plans on having a family from age, about 15-17 years old, or fits a similar description.
I believe I will be a good father but not before 30-35, because I haven't felt it yet and haven't thought about it yet, so I believe I am not a family person.
And as for aging...
Just as Cristale says - after marriage it's all about the two of you.
Do you feel that you want to settle down?
Are you bored with clubbing, traveling or whatever you do recreational?
Have you already had such an amount of experiences that you are ready to turn your back on everything you could call 'adventurous' and give it all to a single human being (and perhaps a couple of other beings later on)?
It's not my goal to be rude here, but starting a family is a big responsibility and once you 'I do' the result of that will be a foundation for raising a kid - a separate life that relies entirely and solely on the environment you have set at home and the overall happiness in this marriage.
Of course, no one knows how things will turn out, but there is one thing I know for sure - I had my fair share of seeing broken families and broken people without childhood and smashed psyche, because of immature decisions.