I promised my husband a baby, but I really do not want a child right now. Am I selfish?

My husband wants a child, but I am not ready. I thought after graduating from college I would be, but I am not. My husband and I have been together for five years and married two years. He is in the Navy so our time is limited in regard to conception time frames. I really want to get my Masters in Social Work, but he thinks I am getting old and I should put my Masters off until after we have a child. I am 25 and he is 27. I always thought I would be ready for kids in my mid-twenties, but now I love our life so much. We have a strong relationship and get along great. I bring the topic up on occasion and then we debate the subject (pros and cons). I want to advance in my career, but I do to some extent feel like I am being selfish. Both of our families are always asking if I am pregnant yet. I love to shop and go out to nice restaurants. The more I look into the more I am deterred. 529 plans, in home child care, cost of elementary, intermediate, and high school are so expensive. I told my husband our child attending good schools are important to me (So they can get into a good college) and so is child care (non-live in nannies are around 300-800 a week). I don’t think we can afford it right now with my student loan and saving for a house (We only have student loan and car payment). He says he will leave things alone, but by March 2011 I need to be pregnant. All the working mothers please help me persuade my husband to wait until I am 30. Any advice would be appreciated.