It doesn't really matter how long they've been on the vine. Some varieties take longer to ripen than others. I hope you didn't pick all of them at one time, without first sacrificing one, to see, if it was ripe.

No, didn't pick 'em all, but have been picking about 1 or 2 a week for a few weeks now and none have been ripe inside. Something is wrong I believe. Everything I have read says it only takes 2 weeks tops on the vine to ripen, and that if the bottom is creamy yellow, as opposed to white, and the tendril and spoon are brown... then it should be ripe. Mine have not been. I don't know if improper fertilization is the problem, or too much/ little water. It is just strange that the plants are growing SO well, and producing so many large melpns, but none completely ripen.

Two weeks on the vine to ripen is way off. Mine take 6-7 weeks from pollination to ripe. That's for Star Brite a 25 lb watermelon.

The brown tendril doesn't always work. Last year using that method most of mine were over ripe. This year it's working fine again like usual.

If you've had the extra rain that the rest of us have had, some of
your melons may never fully ripen. I've got a field of fully grown melons with dead vines, that will never fully ripen. This has been a hit or miss melon year for most of us.