Basically apostrophes are never used to separate a word from a normal suffix in this kind of novel or unusual construction. Pretty much just use apostrophes for contractions and (most) possessives. Example: 90s, not 90's.
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Edit: In English, for English words. Some languages, either those normally rendered in Latin script* or transliterated into it**, make use of apostrophes either to modify an adjacent phoneme or to indicate particular sounds or a glottal stop.
* English-like letters and punctuation
** Like Japanese written as if it were English, for example "Ohayo gozaimasu" which is written in hiragana as おはようございま.
Source: Amateur with the dangerous amount of a little knowledge
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Edit2: Others point out (correctly) that referencing the 1990s as a decade would be properly written as '90s, which is still a use of an apostrophe for a contraction.