BOSTON — A handful of Massachusetts lawmakers are hoping to persuade their colleagues to support a proposal that would make the state the first to adopt a ban meant to eliminate the use of tobacco products over time. Other locations have weighed similar “generational tobacco bans,” which phase out the use of tobacco products based not just on a person’s age but on birth year. Under a Massachusetts law signed in 2018, the age to buy any tobacco product—including cigarettes, cigars and e-cigarettes—was raised to 21.