Voluntary hysterectomy

I know I could get my tubes tied but I dont see a point because I'll still have a period. I'm 22 and I've always wanted a hysterectomy but because I didn't have a child no Dr would do it. I got pregnant on birth control and I have an 8 month old now. My friend said they won't do it until I'm 25. I dont think that's fair. How can I convince a dr to perform one? In just not a kid person. I love my son but I do not want anymore kids or a PD.