I'm sure others know more than me, but you know I have to interject
If I remember correctly, they don't get too big. maybe half a baseball sized at most. My suggestion would be to err on the side of eating it young. It'll only be sweeter and more tender. However if it over ripens, it won't be very good and you'll be eating flower buds...
that reminds me...
Keep an eye on the buds and that will tell you something. If they start to look like they are spreading apart and/or opening, cut it an eat it!