Harvard researchers have found that doctors out of medical school for more that 20 years aren't as up with current treatments. Although those in practice for 20 years have knowledge that can'tr be measured. Also they have a higher trust level from patients.
http://www.boston.com/news/globe/health_science/articles/2005/02/15/greater_risk_seen_with_older_doctors/
http://www.boston.com/news/globe/health_science/articles/2005/02/15/greater_risk_seen_with_older_doctors/