Referring to decades

When you are writing, do you sometimes make reference to decades? This can be confusing because you can choose to use words or figures.

Example in words:
When he ran the London Marathon, he was in his seventies.

Example in figures:
The Beatles were an iconic band of the 1960s.

If I had a tenner for every time I've seen a rogue apostrophe in a decade with figures e.g. 1960's, I'd be a rich proofreader. Please, just don't do it.

If you're writing about a particular decade, say the seventies, then write it in these forms:

the seventies

the 1970s

But don't write: the '70s.

Use the form in words when you are referring to the specific cultural, political and social conditions of that decade:

The radical Bloomsbury Group of the twenties included figures such as Virginia Woolf.

Use figures when it simply labels a time span:

Cinema-going became immensely popular in the 1920s.