If they meant decades, the apostrophes should be where the abbreviations occurred ('20s, '30s, and '40s). If they meant age, none are needed at all as, unlike Dutch, you do not use apostrophes to pluralize in English. Thank you for reading my pedantic comment!
If they meant decades, the apostrophes should be where the abbreviations occurred ('20s, '30s, and '40s). If they meant age, none are needed at all as, unlike Dutch, you do not use apostrophes to pluralize in English. Thank you for reading my pedantic comment!