The demise of the late-night service is a loss for late-shift workers and those who stick around to see the bars close. And it highlights a conundrum that crops up regularly here: In a city that has had a demographic shift toward youth, why has Boston’s late-night scene lagged?

“We’ve never been a fun city, for good reason,” said Robert Allison, a history professor at Suffolk University. “ ‘Early to bed, early to rise, makes a man healthy wealthy and wise’ — and a Bostonian said that.” (Benjamin Franklin was born in Boston.)

Ending the late trains has reignited this city’s tortured, if affectionate, debate over how big or small, cool or quaint, or global or provincial it really is.

“Boston always has a reputation as a small-little-town-type city, and I felt like having late-night T was, like, ‘Whoa, we might be getting on that world-class stage that we always like to talk about,’ ” said Mr. Haro, who pleaded for the late hours at a public hearing. Early on Saturday, he took a selfie with four of his friends to mark one of their final late-night descents into Downtown Crossing station. Recounting the experience in an interview later, he added, “I thought it was a turning point in the right direction for the city, and I was disappointed that it was going away.”

With its high concentration of universities, Boston’s median age is 31.3, according to the 2014 estimate from the American Community Survey; New York City’s is 35.7; and San Francisco’s is 38.6. According to the Boston Redevelopment Authority, adults ages 18 to 34 made up 39.4 percent of the city’s population, up from 25.6 percent in 1960 (though slightly down from 1990).