You should be pruning in late winter and you must leave some of last years wood in order to get fruit. If you prune off all of last years wood, you will get nothing. You can tell the difference between one yr and older wood by the color of the bark.

That movie "A walk in the Clouds," is about a vineyard that catches fire. The family is devastated because they brought the old stock from Italy, and it got destroyed. One scene, our hero pulls and pushes and gets the burnt stump out of the ground. The old grandpa takes a knife, and peels away the bark, and the inside is green! They all rejoice!! I think if you could graft another varietal (like Interior D suggested) onto the root stock it may be easier and get you what you want. Good luck!

Pretty darn impressive and a clever way to grow it. We have some wild grapes here (muscadines) that are about twice as tall and twice as thick as that. I'd guess ~80 feet up into crowns of forest trees.

Where are you located? Grape vines here live for many decades and never die back to the ground! But they do need consistent pruning each late winter or early spring. A 3 year old vine is not a particularly "young" plant and should be ready to bear now. Your grape was likely already at least a year old when you purchased and planted it maybe even older. The first year in the ground you need to remove flower/fruit to allow proper establishment and the development of the root system. And the second year, it may or may not produce any flowers or fruit anyway. By year three (at least a 4 y.o. vine) you can let it fruit but do not let it produce heavily. Thin out the clusters so that each has 12-18 leaves supporting it or roughly each cluster about 18-24" apart.