If you do start lopping off some old data, make sure you announce it ahead of time. Basically everyone's percentile will fall when the guys that got gunned 2-3 years ago throwing 67 and never pitched again are excluded. There could be some bruised egos when a kids percentile falls from 85% to 70%.
On a serious note, there is no telling what findings and observations you could make with the data. As Midatlanticdad mentioned, exactly what a single individual would do with that data is not real clear, however in a macro sense, there could be some good findings which could prove useful.