Daniel Queliz was shot in the neck as police broke up protesters who want to remove Maduro from office over a spiraling economic and political crisis, AFP reported.
He died early Tuesday in the northern city of Valencia, the state prosecution service said.
It said 40 people will be charged for "acts of violence" in Monday's unrest.
Maduro is fighting efforts to oust him as Venezuela, once a booming oil exporter, flounders through severe shortages and the world's highest rate of inflation.
Monday saw the fifth day of clashes this month in the South American country, home to the world's largest oil reserves.
Riot police in Caracas and other cities fired tear gas and water cannon at stone-throwing demonstrators, whose leaders vowed to keep up pressure on Maduro.
No major protests had been announced for Wednesday, but opposition leaders called for huge rallies on April 19.
Another 19-year-old protester, Jairo Ortiz, died on Thursday last week after he was shot in the chest when police broke up a demonstration in Caracas. A policeman has been charged over that killing.
Maduro supporters staged their own rally on Tuesday.
The opposition is demanding the authorities set a date for postponed regional elections.
They also want a referendum on removing Maduro from power.
The opposition is also furious over moves to limit the powers of the legislature and ban senior opposition leader Henrique Capriles from politics.