Hmmm . I think you probably shouldn't wait. I know you are suppose to be more acidic as you age but here is an example in my world where I just don't see it
Grandmother had my uncle, Mike , at 40 (Had two girls in her 20's )
My aunt had my cousin Joseph , at 40 ( Had first boy at 38)
My aunt had my cousin , Jon, at 40 (Had two girls in late 20's and early 30's)
My friend had her son at 40 (had first son at 38)
Another friend had her son at 40( had two other boys in her 30's)
Another friend had her son at 40. ( had a girl at 34 , a boy at 36 , another boy at 38)
Another friend had her daughter at 40. (had two girls both after 35)
Another friend boy/ girl twins at 37.
Another friend had a girl at 40, boy at 42 and a boy at 47!
I just don't see how being old helps in having a girl. SO if I were in your shoes I would just do it at 37. Oh , I got pregnant at 37 and it was a boy.
I so hope you get your girl!!!! I wish I had pink dust , sadly I don't .
Although , now that I look at it I have some damn fertile family and friends!!! Yea mature mamas!!!!