Options for permanent birth control

So I'm currently 23 and I'm having my last kid. I have a 4 year old step son, a 19m old son and I'm pregnant with my little girl. After she's born, I'm done having kids. I've heard that unless you're a certain age, most doctors won't give you any type of permanent birth control. I've known this is my last baby and I'm done after she's born 100%. Three kids is enough for me. Any advice on what I can do?