on this chart of bannana ripeness:

you should marry a woman at banana level 4 and inseminate her at banana level 5 then continue getting her pregnant until level 7 and stop

i would estimate banana to girl conversion as follows:

4 = 12 y/o

5 = 15 y/o

6 = 18 y/o

7 = 25 y/o

this gives her 10 years to pump out babies that should give you maybe 7 or 8 kids