i wanted to have kids in my late 20s due to my career choices, etc, but lost one at 27 and one at 29 that drove me to a full blown PPD that wasn't diagnosed until a year later. Between healing emotionally, having the relationship ready to try again, some months of unprotected sex with no baby, we are currently on a break and in our early 30s.
I think our children decide too when they want to come.
My plan was to have them before i turn 30, mostly as my parents had us late and i felt the weight of their aging much sooner than most of my friends, as my parents are 10 years older than my friends' folks. but my kids had other plans. and you have to play along.
i think waiting for financial, career and especially emotional stability/maturity before having a baby is definitely a good thing, yet in the society of today it takes a bit of a toll on couples (and women more than men). In a sense: i think my parents had a huge gift to have their parents young, fit, healthy and ALIVE when they hit their 50s and their 60s even. When i think of my siblings and me, our folks would need to be some pretty damn fit 90-100 year olds for us to have that same luxury. That i think is the thing that sort of saddens me the most (and not so much when i think of the length of life, but of the quality of it).