I was curious enough to look through the medical literature. There have been controlled studies in older men; these studies were pooled and looked at in the following article:
J Gerontol A Biol Sci Med Sci. 2005 Nov;60(11):1451-7.
Adverse events associated with testosterone replacement in middle-aged and older men: a meta-analysis of randomized, placebo-controlled trials.
Calof OM, Singh AB, Lee ML, Kenny AM, Urban RJ, Tenover JL, Bhasin S.
Boston University, School of Medicine, E201, 88 E. Newton Street, Boston, MA 02118, USA. firstname.lastname@example.org
They identified 19 studies that met these inclusion criteria: testosterone replacement for at least 90 days, men > or =45 years old with low or low-normal testosterone level, randomized controlled trial, and medically stable men. These studies contained 651 men treated with testosterone and 433 with placebo. Prostate events was significantly greater in testosterone-treated men than in placebo-treated men, including rates of prostate cancer, prostate-specific antigen (PSA) >4 ng/ml, and prostate biopsies. Testosterone-treated men were also four times as likely to have hematocrit >50% as placebo-treated men.
The link is www.ncbi.nlm.nih.gov/pubmed/?term=J+Gerontol.+2005%3B60%2811%29%3A1451%E2%80%937