There is very little on the internet that directly addresses directly anaesthesia and the elderly.
The American Geriatric Society has a web site that publishes a number of clinical guidelines and recommendations for the care of their elderly. The Journal of the American Geriatrics Society provides on-line abstracts.
Interesting abstracts: Rasmussen 2003 Postoperative cognitive function - GA vs. LA. Eurosiva abstract by Rasmussen on the same topic. Barry Baker 2003 performance decline with ageing.
UC Irvine provide a PDF resource titled "Perioperative Geriatrics".
There is probably no consensus as to what makes a geriatric patient but it is generally accepted that physiological age is far more important than chronological age and that older patients are "dissimilar, making individualisation of the anesthetic technique mandatory"(McLesky, Geriatric Anesthesiology).
The presence and severity of comorbidities is a much better predictor of risk than age itself.
Ischemic heart disease, dementia, diabetes, CHF, renal insufficiency, and emergency surgery have been correlated with poor outcome in the elderly. The number of medical conditions a patient has correlates well with complications as well as the ASA Risk class. The healthy geriatric patient should not be denied outpatient surgery unless the surgery is complex or prolonged and issues such as resources at home may determine the need for admission.