Answer: It's a good thing you like apples! Normally you would watch for any suckers from the ground below the graft and remove them right away so that all the energy from the roots goes only into the grafted top. From your description it sounds like the rootstock may have overtaken the grafted top, meaning the top has either died off or been supplanted by a sucker (or several suckers) from the roots.
Sometimes on a neglected tree the bark or foliage or blooms are different on different sections and you can tell that way which is which, but sometimes they are all the same and so you would suspect the original grafted top has disappeared. If the grafted top is completely gone cutting it back now will do no good.
Once the sucker has taken hold in a big way (it sounds like this one has) you might do so much damage to the tree removing it that it would cause a forest of suckers from the roots and cause more problems with the trunk itself. At this point, you might just leave it alone and treat it like a regular apple tree, especially if it seems healthy and you like the way it looks.
Apples ripen at different times depending on their variety and some are quite late. Size also varies between varieties and they will be smaller than normal in a dry year. You can tell if they are ripe (and thus as sweet as can be) by looking at the color of the seeds -- they should be pretty dark. If you plan to treat it like an apple tree and would like a better crop, you might want to check with your local County Extension for the best routine and correct timing for routine preventive apple care in your area.
Enjoy those pies!
Q&A Library Searching Tips