When is it ok to be jealous?

I admit, I have a plan. I want my Master's degree before I start having kids. I just think that it will be better then trying to juggle doing that and raising kids. ...but...I see pregnant people, and I am jealous. I see people with babies, and I am jealous. I see my nephews, and I am jealous. I want one. One of my own. I almost feel selfish. ::Sigh:: I know that my dad has my back...most other people in my family would be ok if I got knocked up. My husband keeps telling me that I am running out of time. I am older than him so I see where it is coming from...still I know I am on the right track...