Answer: Based on your description I suspect the vine you have was grown from seed rather than grafted using material with proven flowering ability. Seedlings can take as long as 20 years (or more!) to bloom. There really isn't too much you can do to hasten it along as it needs to mature. One suggestion though is to make sure you are not oversupplying it with nitrogen fertilizer as this can encourage vegetative growth rather than flowering. I wish I had a magic solution for you, but basically it will eventually bloom when it is good and ready.
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