I will echo Steven's response and go a bit further for clarification. First, ripen does not necessarily mean ready to eat (I have never seen them ready to eat right off the vine). Ripen means ready to harvest (you should harvest when the fruit gets a little lighter green in color and the base of the fruit swells and will bulge a little with some very slight separation and yellowing at the outline of the hard "plates"), where you will let them sit on your counter till it becomes ready to eat (which usually occurs in sections). You should only eat the portions where the "plates" fall off or are easily flicked off (for a better term). Just scrape the luscious fruit off the core. There are tricks to speed up ripening or to try and get the whole thing to ripen at once (but in paper/plastic bag or wrap in foil) but be careful as the flesh can go quickly from ripe to fermented.
From Julia Morton:
"Season
Flowering and fruiting overlap because it requires 12 to 14 months from the opening of the inflorescence to the maturity of the fruit. Therefore, there are often unopened inflorescences, immature fruits and ripening fruits together on the same plant. The current year's crop is ripening through summer and fall while the following year's crop is forming beside it.
Harvesting
The rind is always green though it assumes a lighter shade as the fruit matures. The fruit, with at least an inch (2.5 cm) of stem, should be cut from the plant when the tile-like sections of rind separate slightly at the base, making it appear somewhat bulged. At this state, the fruits have been shipped to local or distant markets. If kept at room temperature, the ceriman will ripen progressively toward the apex over a period of 5 or 6 days. The flesh should be eaten only from that portion of the fruit from which the rind segments have so loosened as to be easily flicked off. To ripen the whole fruit at one time, it should be wrapped in paper or plastic, or possibly aluminum foil, as soon as cut from the plant and kept at room temperature until the rind has loosened the entire length of the fruit. At this stage, it will be found that the flesh also falls easily away from the inedible core. Once ripened, the fruit can be kept in the refrigerator in good condition for a week or a little more. Rinsing off the floral remnants improves the appearance of the flesh, but it does cause some loss of juice."
