How can an old Apple ID be merged into the newer ID?
Solution 1:
As of now, you cannot merge multiple Apple IDs into one Apple ID. It has been rumored but it is not possible at the moment.
Solution 2:
Apple still working on it. I know about it from last news.
http://www.macrumors.com/2011/10/18/apple-still-working-on-allowing-merging-of-apple-ids/