Hi there,
I'm not sure if what you're feeling is empty nest syndrome exactly -- typically, that syndrome involves raising children then feeling lonely and abandoned when they leave home. I think what you're feeling is a very natural urge to hav kids, and that's perfectly normal, as far as I know!
It seems logical that we want kids eventually -- after all, reproducing is the most basic part of our existance, right? I guess it gets tricky when you feel like your time has come, but you're too young, not stable enough or too "immature" according to the people around you. Sounds like that's the case for you, and I'm sorry to hear it. Don't worry, though! I think what you're feeling is pefectly normal, although it sounds like you'll need to be patient and let your family and your boyfriend come around to the idea.
In the meantime, I would suggest doing everythign you can to get your life ready for children and show your family that you're responsible enough to have children through the way you live your life. Good luck, and I hope everything works out for you in the end!