Consider using the Domain Age Tool to research that factor when investigating a website. The tool's quite simple to use. Just plug in a URL (or several at a time), click the "submit" button, and you should get back a page showing the site's exact age in months and years.
sba.gov 13 years 7 months old
nyssbdc.org 11 years 2 months old
whitehouse.gov 14 years 1 months old
microsoft.com 14 years 3 months old
mcdonalds.com 14 years 2 months old
pg.com (Proctor and Gamble) 14 years 3 months old
timesunion.com 12 years 1 months old
nytimes.com 14 years 2 months old
Yet there are some, such as ibm.com, walmart.com, and state.ny.us that it is Unable to Determine.