Without it being complete, there's little chance of telling the age. It appears to be a broken slate preform. In some lithic poor areas (primarily in the Northeast) they often had to resort to using unusual materials like slate for points and tools. Ground slate items are not uncommon up there and believe it or not, they actually make great points, knives and other tools. To fashion them, they would roughly knap them to a shape and then grind to form. The same method is used for making shale gorgets and small hematite celts here. Yours looks like it could have been one that was broken during this process.
The point is broken in half...i'll try to show it in the picture. it was found in an area abundant in flint arrowheads, pottery and other tools. It was found near well known camp sites of the recent lenni lenape tribe...the munsee. but there has also been evidence of much older tribes living in this area.