I keep coming across writers – writers: people who delight in the manipulation of words – who render someone’s age as “40’s”.
Why? What is that apostrophe doing?
An apostrophe stands in the place of some text commonly acknowledged to be missing. (I live on the outskirts of So’ton, where the apostrophe is commonly acknowledged to cover for the missing “uthamp”.) In the case of the age, we are looking at a plural – indicating any one of the years of a decade. In this respect, forty is treated like pony. The plural ends in ies: ponies. What’s missing? If we wrote it pony’s, it would be a possessive: the pony’s saddle. The text commonly acknowledged to be missing in a possessive is “his”, but it’s so long since anybody used “the pony his saddle” in full that the long form is in total disuse. The only place I can recall ever coming across it is in Robert Louis Stevenson’s Treasure Island where the account book of the pirate Bill Bones refers to his share of the loot as “Bones his pile”, but Stevenson was using a deliberate archaism to make the character sound piratical.
Back to the case in point, is 40s a possessive? No, of course it isn’t. Forty does not claim ownership of anything. The age is the thing possessed, in this case by a person in the character list of a play. You can see that if you write out the character description in full, where we can see the age being conveyed by “his”: George, an engineer in his 40s.
The objection here is that writing the ess next to the zero looks odd. Fair enough, but if you can’t bear to write a letter next to a numeral, then write out the word forties.