Injection drug users (IDUs) who have recently initiated an injecting career have high risk behaviors for HIV infection. The average age of an IDUs first injection is typically reported as 19-20 years, and some literature has reported 'maturing out' of drug use typically around 40 years old. The purpose of this study was to discriminate risk behaviors among newer injectors by age of initiation. This cross-sectional study includes volunteers enrolled using extensive community recruitment techniques in 1988 and 1989 in Baltimore, MD. Of the 722 injection drug users who had initiated injection within the prior six years, 124 were over 35 years old of whom 53 were 40 years and older. Rates of HIV were lower among those over 40 years (13.2%) than those who were 35-39 years (22.5%) or under 35 years old (20.9%). The behavioral characteristics of those aged 35-39 were similar to those under 35 years old, but those over 40 years old when compared with less than 39 years reported injecting at least daily less frequently (88.7% vs 76.5%, p = 0.042), using a needle from a sterile wrapper (19.0% vs 36.6%, p = 0.006), and injecting with their own works (52.6% vs 28.8%, p = 0.021). This study shows that people initiate injection drug use across a wide age range and that needle hygiene practices early after initiation tend to be safer in older compared to younger initiates.