Ignorance/irresponsibility + sex = children = unsuitable for raising a child
Forethought + sex <> children = suitable for raising a child.
In general, of course. In many cases, the child isn't expected and the parents are suitable to raise a child. And of course, those that wait for the ideal time doesn't exclude those that have a child early and feel it is suitable.
The way I see it, if you are able to talk to your mate about having children (the big issues involved), if you talk about the financial and practical stress you are going to be under and if you actually do some semblance of preparation for the child, you are probably going to be a fine parent. The rest is just gravy - there is no ideal situation... but if you can't generate some sort of plan for the practical aspects of the biggest responsiblity of your life, chances are you aren't responsible enough to have it.