A somewhat strange myth has taken hold in some precincts of American conservative opinion that some vast swathe of the population isn't paying taxes. In fact everyone pays sales taxes and other state and local taxes, and as Adam Looney and Michael Greenstone write for the Hamilton Project almost all working-age people pay federal tax on their income.
The main bloc of people who don't pay income or payroll taxes are elderly people. Old people tend not to work, and many old people don't have much in the way of investment income either. But it's not like they're freeloading, they're just people who paid taxes in the past when they were working.