Domain age and length of registration, (as confirmed by Matt Cutts) in itself, do not impact ranking. An old domain is worth it, if and only if,
- It has a good number of relevant, authority backlinks
- It has a high PR
- It is a reputed domain (i.e. it enjoyed a good search ranking)
‘Age’ in itself, does not guarantee rankings. A 10 year old parked domain that will have zero impact on your website's reputation.
Also, in it’s latest blog, Google has clearly specified that it prefers not to show parked domains that are seldom useful, often filled with ads and typically don’t have valuable content for our users.