In my experiences, I don't think this is true. I have sites for which I pay for a Yahoo listing... and sites I don't... I notice only a barely perceptible increase in Yahoo traffic for sites which have a Yahoo directory listing. I do wonder, though, whether sites with a Yahoo directory listing get more "trust"... even if not more direct traffic. In past (and here I'm speaking about last 1-2 years), the Yahoo listed sites just generally do better. Part of that might be related to Yahoo directory listing. Or it could be a conincidence.... (I tend to spend more money wantonly on sites that do better... )
I think yahoo is looking for quality content...Google updates my blog in few days but for yahoo it takes 2-3 weeks , i don't know why....it seems that they are not giving more importance for back links as google gives.
Age of domain does NOT appear to matter. I just built a few sites where they are keyword rich and where the domain name has the keyword in it. I did very little linkbuilding, and the domain is just months old. Those sites catapulted to the top 5 spots in each case, and in fact surpassed my 11-year old website that does not have the keyword in the domain name. Age of domain don't mean nothing to Yahoo.
I think a combination of having great content plenty of backlinks and proper use of keywords will rank a site well in yahoo.