If i become a Sports medicine Doctor, My "life" will Begin at a late age?

Your potential fertility is too unpredictable to plan your life around. You could have 3-4 kids starting in your 30s. You could also start trying in your early 20s and find you are infertile or have difficulty conceiving or carrying a child. You could have one or two in your early 20s and find out you have a tumor and have to get a hysterectomy, or the first birth could cause a uterine injury that makes it impossible to carry more. Go for the career you want and worry about kids when you are good and ready for them. Whether you have one or ten, or if they are even all biological or some adopted, you will be happy with them.