Maybe Big Pharma has something to do with it by medicalizing lower sex drive or lower “performance” that occurs with aging and charging the men up with Viagra.

An article in the Times (London) has this take on it.

...[U]ntil the 1980s, when doctors in the pay of the pharmaceutical industry began using the term erectile dysfunction to describe impotence as a medical condition, it was well recognised that such failures affected most men at some time in their lives, and that sexual performance generally declines with age. As erections happen spontaneously during sleep in healthy males, many doctors took the view that impotence was largely psychological, or a natural part of ageing.

...[A]nd in the US, a rise in HIV in elderly men has been attributed to it, though Pfizer has so far resisted demands for safe-sex warnings on packaging.

...[R]ates of sexually transmitted disease in pensioners are increasing in affluent retirement communities where invigorated elderly men finding themselves shunned by their elderly wives are picking up prostitutes. “You get them cruising the red-light area looking for prostitutes and contracting venereal diseases,” says Felder. “Not surprisingly, that too leads to divorce.”

http://www.timesonline.co.uk/tol/life_and_style/health/article2060810.ece

Ah, Baloney…all they tell you is how.
Hell,I know how. I need to know WHO?