As a guy who came of age during the cutoff era, let me give you the low-down on these.
In the 60s, only boys would wear denim shorts, and they were always cutoffs. I think the kids on "Flipper" made them somewhat respectable, but even there, they were mostly for swimming and such, never for when they needed to be presentable.
In the 70s, it started becoming acceptable for young men to wear shorts in more situations. If you look at photos of
Woodstock (1969), you'll see a lot of shirtless guys in long pants - it just wasn't that common for guys of college age and older to wear shorts. But in 1970 or maybe 71, my high school changed its dress code to allow guys to wear shorts and sandals, but only in the month of June.
The problem in the early 70s is that the shorts that were available were mostly either tennis whites or Bermuda shorts, the latter being either too preppie or too Bob Hope/Jackie Gleason/Lou Costello. So cutoffs started becoming popular. And any guy who could cut a 2x4 to length could cut a decent pair of cutoffs (PP notwithstanding). They were also macho, the only shorts that construction workers could wear on the job, and at least giving the suggestion of having once been jeans with holes honestly worn into the knees, from either rough work or rough play. Eventually it became possible to buy them pre-cut, with neatly frayed hems, but I don't think I ever bought them that way (and if I had, I wouldn't admit it).
Around the same time, shorts for me got shorter, and continued into the 80s. I'm not exactly sure why. Perhaps it's in reaction to the way knee-length shorts were portrayed by comedians in the 60s, or counterbalance to the preppie look, or maybe it's just because it's easier to do a decent job of cutoffs at mid-thigh than at the knee. But get short they did, and if you don't think they can look macho, you haven't seen
"Magnum, P.I."
Somewhere along the way, some bright marketeer at a clothing company decided that they weren't selling enough cutoffs, and the reason was that they looked too rough, but if you could get them hemmed ... wow, what an idea! And that marked the beginning of the end for jean shorts on men. They did become popular for a while, and that's why you may still see guys in their 40s and 50s thinking they're ok. But getting them store-bought and hemmed destroyed the illusion. I've never worn hemmed jean shorts, and never will. (If i could fit into my old cutoffs, I'd wear them, at least for gardening, but I can't, and I'm not foolish enough to make a pair out of jeans that currently fit me.)
But I still do wear shorts that are a few inches above the knee. I'm convinced that some aspects of our style sense are burned into us when we develop it in our teens and twenties, and it's very difficult to change, harder for some than others. Shorts on men that cover the knee may look good to people who were college age in the 90s and 2000s, but to me, they'll always look like Bob Hope or Jerry Lewis pulling off a sight gag. Conversely, folks from that era may think that Chevy Chase's shorts at the end of National Lampoon's Vacation (the original, from 83) were part of the gag, but they weren't - that's what men wore at the time.
There are no absolutes for this sort of fashion question. There's only "these are the styles that are/were popular at such and such time" and "this is the way I react to such an such styles, because of the era in which I developed my clothing sense."