It depends on the specialty, and the willingness of the older doctor to adapt to change. Older doctors are the most experienced, they've seen a lot of different types of cases, and they've had time to perfect their technique. The problem arises in specialties that change quickly. The younger doctors, as a whole, are much more likely to be willing to stay up-to-date on advancements in the field, and have been trained with much more updated technology and techniques. The older doctor often gets stuck with what worked best 30 years ago.
I have met a few exceptions to the rule on this, but I have personally opted against the service of several older doctors because they refused to do anything differently than when they got into the profession in the 60s or 70s. Thanks, but I'd rather take advantage of a modern standard of care. This isn't so bad for my family practitioner, but maybe not the greatest thing for a neurosurgeon.