This is a difficult question to answer, for the simple reason that not everyone agrees on what a genre actually is, and because 'longevity' is also quite elusive.

What is rock'n'roll? Are Jerry Lee Lewis, The Supremes, The Sex Pistols, Bruce Springsteen and Black Sabbath all in the same genre? Elijah Wald's book How The Beatles Destroyed Rock And Roll argued that the original rock'n'roll actually died in 1965-1966, because the album-focused progressive, artistic genre that the Beatles ushered in with the likes of Sgt Pepper was a very different beast to what was essentially the fun, upbeat dance music being made by Elvis and Little Richard.

You see this issue in jazz, too - there's a world of difference between the comical sound-effects-heavy early jazz getting recorded in 1917 and the elegiac, almost classical suites of Duke Ellington in the 1950s, or the immaculate, not particularly swinging, improvised music of Keith Jarrett in the 1970s. There are certainly historical links between the people making those different kinds of music - Keith Jarrett played in Miles Davis's band at one point, and Miles Davis played for a long time with John Coltrane, who'd recorded an album with Duke Ellington. Duke Ellington also recorded albums with Louis Armstrong, who saw live shows by Buddy Bolden, often claimed as the originator of jazz). But are all of those very different sounding things really the same genre just because there's a historical link? The same goes for rock'n'roll - different things get called rock'n'roll at different times - The Supremes got called rock'n'roll in 1964.

Similarly, there's country songs (e.g., Waylon Jennings' 'Are You Sure Hank Done It This Way?') that complain about how country these days ain't like it used to be in the days of Hank Williams - and commercial country music didn't sound much like Hank Williams in the 1970s when Jennings recorded the song. But, well, Jennings had started off as a rock and roller, playing in Buddy Holly's band, and his version of country music was a little bit rock and roll. And this was well before the era of Big & Rich and Florida Georgia Line (who sound much more like rock and roll than country to me, apart from the twang in their voices). I mean, people would probably call Coldplay 'rock', but this Big & Rich song has more in common with Black Sabbath than Coldplay do, sonically.

Longevity is similarly hard to pin down. Certainly, single acts like Black Sabbath can still draw a crowd close to 50 years later. I mean, Tony Bennett - the crooner, who sang with an army band as a drafted soldier in World War II - still draws a crowd - he played at the ~2500 seater Riverside Theatre in Milwaukee the other day, in fact. But does the existence of some old guys still doing their thing mean that the whole genre itself is still lasting? You could argue that Black Sabbath or Tony Bennett are mostly playing to crowds who already liked them in 1974 or 1957, respectively, and who just haven't died yet.

And of course, there are some very old forms of music which still get played to large crowds relative to the genre's heyday. One of the big churches in the city I live in, for example, has an upcoming concert playing versions of the Renaissance-era music of the likes of Thomas Tallis, who was born over 500 years ago. Seeing as that music was often music meant to be played in big old echoey churches, and such events are still popular - probably more popular than the regular services - you could certainly see that as playing to large crowds relative to a genre's heyday.

Similarly, the song 'Nottamun Town' is usually thought to date from the late-medieval era. It had somehow survived in the Appalachian folk community to the present day (e.g., a recording here played in the early 1960s by Jean Ritchie, who learned it from her Appalachian family). The melody of 'Nottamun Town' was used in a Bob Dylan song called 'Masters Of War', and there's a Ed Sheeran cover of 'Masters Of War' on YouTube with 2 million views - which is magnitudes larger than the size of the crowd who would have been able to witness a single performance of 'Nottamun Town' in the year 1600. Is an Ed Sheeran cover of 'Masters Of War' broadly the same genre as a late-medieval rendition of 'Nottamun Town'?

In the end, it depends on how you define genre. Certainly there's some cultural aspect to a genre. If we say that country, or jazz, or rock are genres, it means that genres are about the people who make it and listen to it, and the way they use that music. If jazz actually is a genre, it's more about ways of thinking about music than the sounds of the music itself, because the Original Dixieland Jass Band sound a world away from Keith Jarrett, but both get called jazz. Does the culture around Ed Sheeran think about his cover of 'Masters Of War' in largely the same ways that Jean Ritchie's culture thought about 'Nottamun Town'? Did the way Jean Ritchie's culture think about 'Nottamun Town' reflect the original use and purpose of the song in the late medieval era?

There's no solid answers here, for better or worse, but it's safe to say that there's lots of old music, and plenty of music with some very ancient influences, that's still being played to healthy crowds.