I’ve always thought that the answer to this should be yes, in primary elections, if they will turn 18 by the date of the general election. This is the law in some states, and now Vermonters will get to decide this issue on their November election ballot.
Section 72 of the Vermont Constitution reads:
At the biennial session of the General Assembly of this State which convenes in A.D. 1975, and at the biennial session convening every fourth year thereafter, the Senate by a vote of two-thirds of its members, may propose amendments to this Constitution, with the concurrence of a majority of the members of the House of Representatives with the amendment as proposed by the Senate. A proposed amendment so adopted by the Senate and concurred in by the House of Representatives shall be referred to the next biennial session of the General Assembly; and if at that last session a majority of the members of the Senate and a majority of the House of Representatives concur in the proposed amendment, it shall be the duty of the General Assembly to submit the proposal directly to the voters of the state. Any proposed amendment submitted to the voters of the state in accordance with this section which is approved by a majority of the voters voting thereon shall become part of the Constitution of this State.
Prior to the submission of a proposed amendment to a vote in accordance with this section, public notice of the proposed amendment shall be given by proclamation of the Governor.
The General Assembly shall provide for the manner of voting on amendments proposed under this section, and shall enact legislation to carry the provisions of this section into effect.
Apparently the state legislature very quietly adopted this constitutional amendment, and now it’s up to the voters. Then the legislature will have to craft implementing regulation if the amendment passes.