Justin Bieber was 18 years old for most of 2012, turning 18 on March 1 of that year.

He was born on March 1, 1994, in London, Ontario, Canada, so:

  • From January 1 to February 29, 2012, he was 17.
  • From March 1 to December 31, 2012, he was 18.

So if someone asks “how old was Justin Bieber in 2012,” the usual answer is that he was 18 during that year (with the small caveat that he started the year at 17).

Information gathered from public forums or data available on the internet and portrayed here.