It's generally a good idea to exclude people whom you haven't spoken with recently from your reference list. One risk is that the reference won't have a clear recollection of you or what you did. The other risk is that the employer may wonder why you can't come up with references from your most recent jobs.
If you feel that a long-lost reference is too valuable to exclude, you must make sure that all the contact information is current. Don't be afraid to give them a call either, and ask if they will still be a reference for you. Chances are they will, and they may come to you at some point to return the favor!