this question is a very personal one. The answer to this question depends on what each couple wants out of life. Some women may want to consider that your body recovers faster before thirty. Others may want their decision to be based more on their career track.
Who knows when the best time to have a baby is? Ideally when you have enough money and a good plan set up. But life throws you curveballs when you least expect them so your perfect plan might not be so perfect after all. I would believe being in a stable relationship( having a kid is a lot of work for one!) and having a lot of money in the bank would take some stress out of the situation. But I got pregnant at 20 and was not married and was this ideal no, but would I change it no! It was not the easiest but I had a good partner and a wonderful family. Its 6 years later and I am married with two kids, and there are still struggles that we go through. Not because I had a kid at 21 though! There is no great answer and you will never fully be prepared to have a baby.