We don’t have a figure for the mean, i.e. arithmetical average, age of Las Vegas residents, since census bureaus tend to focus more on the median age of populations. This is the measure that divides the age distribution in a stated area into two equal parts: one-half of the population falling below the median value and one-half above the median value, and is deemed to be a more useful statistic for those concerned with demographics.
According to the 2004 (latest) American Community Survey, the total population of the City of Las Vegas was 536,119, with the median age of the residents being 35.5 years. The percentage of the population that was 18 years or older was 74.6%, almost exactly the same as the national average (74.5%), while the percentage aged 65 and over was 12.6%, which was slightly higher than the national average (12%) -- to be expected in a city that's so popular with retirees. The percentage of the population 85 years or older was only 0.8%, however, which gave Las Vegas a joint ranking of 49th in the nation, according to the survey sample (Honolulu came in first with 3.5%).
