I asked this question myself about a year ago petrosc.
The logic behind it is, an older website is more established and is less likely to be either a parked page or one of those pathetic temporary websites filled with ads.
It's a clever little thing to add to increase search result quality in my opinion, although I dont think it's a very weighted factor.
I personally never tried or benchmarked any domains with google but what i've been informed by monte cahn on webmasterradio.fm, google tend to rate older domains higher than newer ones even though the domain never been developed since been created.