Confusion about the relationship between hyphens and numbers, whether they appear in numeral or spelled-out form, is rampant. Each of the following examples erroneously employs hyphens; discussion after each sentence explains the error, and a revision corrects it.
1. Because of concussions, he had played just sixty-nine games in two seasons between 2010-2012.
Using a hyphen rather than an en dash in a number range is generally an error of ignorance (though some publications, with full awareness of the distinction between the two symbols, confusingly insist on doing so anyway). However, linking 2010 and 2012 in a number range with any connective symbol is redundant to preceding the numbers with between, which should be counterbalanced with an intervening and: “Because of concussions, he had played just sixty-nine games in two seasons between 2010 and 2012.” An alternative revision, correctly employing the en dash, is “Because of concussions, he had played just sixty-nine games in the 2010–11 and 2011–2012 seasons.”
2. This goal may be achievable in a 12-to-24 month time frame.
Just as it is not necessary to repeat the word for the unit of time in “12 months to 24 months”—the first iteration of month is implicit—the word may be elided from a version of the phrase that uses hyphens. But do not link the two numbers with one or more of these symbols (or with one or more dashes); to serves the connective function, and the hyphens represent that the numbers, when combined with month, modify “time frame.” Form the construction (which employs a syntactical technique known as suspensive hyphenation) as shown here: “This goal may be achievable in a 12- to 24-month time frame.”
Also, many publications spell out numbers up to one hundred, so it might be correct (or preferable to you, if no specific style is required for your content) to instead write, “This goal may be achievable in a twelve- to twenty-four-month time frame.”
3. A similar incident occurred four-and-a-half years later.
The words representing a number consisting of a mixed fraction should be hyphenated only if the phrase modifies a noun that follows it. Here, the words in the phrase should stand on their own: “A similar incident occurred four and a half years later.” (Compare “A similar incident occurred after a four-and-a-half-year interval.”)