We did not discover the concept of FI until our first child was born (mom age 36, dad age 38). After reading Robert Charlton's book and Early Retirement Extreme, we committed to FI and have trimmed our middle class fat to be able to save and pay for child care (not a high cost of living area). Husband will definitely be able to retire at age 50 and I may continue to work because I want to, but we will be readily available to our young lad during his middle school years.
So we are going from no plan to FI in 12 years. Not too shabby, in my opinion.
We had a miscarriage after our child was born, but had already developed a budget that would absorb most of the extra costs, mainly child care.
We had our child because we didn't want to be 50 and be sad that we hadn't had one. Of course it's worked out fine. However, despite having waiting until 35 to conceive, I would not want to wait til a very late maternal age before trying just so I could save even $100,000 extra. The risks of serious problems is just so much higher.