Hard question for me there, because I've wanted children since I was about 17. I knew I wasn't "ready", but I desperately wanted them. It's actually been about 6-12 months since I decided I was "ready" and that time was mostly waiting for DH to catch up mentally there. I don't know what caused the change or what makes me feel that way. I've never felt "too young", and if I had accidentally fallen at 18 for eg, I still would have been excited and happy.