In written text, use numerals for the day and year, and the name of the month written in full:

  21 June 2012

No punctuation is necessary, even when the name of the day is included:

  Wednesday 9 August 2017

There is no apostrophe in decades written as numerals:

  1960s

The names of centuries are written in full words or a mixture of words and numerals:

  eighteenth-century porcelain

  15th century (note the lower case ‘c’ for century)