I always find it interesting to look at the power on hours of my drives, but I haven't seen any consistent pattern to it. It's an age indicator, but it doesn't mean anything has failed or is about to. It's like knowing the miles/km (or in this case, also the startup cycles) on a used car, it's nice to know but it's far from definitive. There is some threshold where the manufacturer will flag it as "worn out", but that's not an actual failure. If it's still running perfectly I wouldn't worry about it, but of course important data should always have a backup, regardless.
I generally think of 20K hours as a drive that's becoming "old", but that's just me. With so few start/stop cycles it's probably easier on it.
In my extended family there's drives running daily at 30-40K hours, a pair at 60K hours, even one at over 80K hours with no errors logged.
A few of my drives developed problems at just over 20K hours. Not many less than that, other than lemons who didn't even get close. It seems 3-4 years has been the typical life span of my primary desktop drives - the old 5 year warranties were convenient.
The worst problems I had with drives was back in the late 90s/early 00s. It got better when I started paying attention to the quality of my PSU and drive cooling.
My very old Conner 40MB and 240MB drives still work, but I don't think they were stressed the same as today. No idea how many hours they were used, but I'm sure the 40MB wasn't very many. When it retired, it stayed retired, it wasn't worth reusing for anything.
I remember hating Western Digital because of the terribly short life span of my 1.6GB "Caviar". Found out only recently they were well known as defective.