I'm surprised that Massachusetts didn't already have pre-registration for at least 17 year olds. Indeed, here in South Carolina you can register at age 17 and even vote in primaries at age 17 if you'll be 18 when the general election for that office is held.
I feel like access to voting had to be polarized and politicized for the Mass. legislature to realize this could be a Democratic move.
Our civic culture can be odd. Until 10 years ago, the assembly was essentially ruled by a self-proclaimed philosopher-king who ignored referenda and controlled the Democratic majority through punishment.