I'm not sure about ageing pages that are already in a book. But I'm betting there's some kind of paint or stain (maybe wood stain?) wash you could do over them.
Something I thought of when I read your post was this website http://www.brahmsbookworks.com/
They sell spell books. You have to scroll all the way down to the bottom to see the different kinds. I like the Section Title pages. It kinda reminds me of the illuminated manuscripts of old books, you know?
Not sure if this helps. But good luck!!!!