Batch Thumbs is a freeware product that will allow you to do a massive rename in the matter of a few clicks.
Put all the files in one folder and tell batch thumbs where they are and how to rename them. You will be able to tell the program to rename them starting with P1 and to add one number per file so that you will end up with P1, P2, P3...
Easy as pie.
I personally don't have much of a problem with seeing younger player photos for older players. I figure that we all have pictures of ourselves when we were younger and if I had the choice I would want others to see those instead of my old and balding sorry ass in my 30s.