In New Hampshire, you must be 18 to vote. However, 17 year-olds are allowed to register to vote if they will be 18 by the next election day.
Allowing 17-year-olds to vote in primaries does not violate the 26th Amendment, which only forbids states from setting a voting age older than 18.
Almost half of US states, including Maine and Vermont, accordingly allow 17-year-olds to vote in primaries if they will be 18 by the time of the general election.
Pro and Con
Those who support allowing 17-year-olds to vote argue that including them will encourage civic involvement among youth.
Those who oppose allowing 17-year-olds to vote in primaries often argue that younger voters are less informed at the polls. In 2011, then-House Speaker Bill O'Brien supported limiting the voting rights of college students for that very reason, arguing, "That's what kids do, they don't have life experience, and they just vote their feelings."