EM Pulse Source
The only thing that would reliably prevent electronics working (albeit not electricity per se, which doesn't seem conceivable) is an electromagnetic pulse. If an international conflict involved an arms race over EM weapons and then something went catastrophically wrong (think Dr Strangelove), then you could conceivably have some weapons pile or malfunctioning device which sporadically gave out an EM pulse, re-frying any electronics that anyone attempted to re-create.
A world without electronics
Electronics underlies all long-range communications; since the beginning of the 20th century we have made it an increasingly necessary part of our lives. Without it, we would be back to 19th century methods of transport, communication, etc. We would have an awful knowledge of what things could be like, but unreachably.
Electricity itself would work, but without electronics it is very difficult to control it beyond on and off. It would be flickering-light-bulb technology, not communications beyond essentially morse code.
Look to the Amish
There is apparently a rule against using electricity among the Amish, which has sent some to recreate the ability to plug into power in a wall socket with pneumatics; by running a compressor (even manually), a series of pipes can run the compressed air to where it is needed; it is simply a different method of power transfer. So some parts of life might not look too different.
Indirect technology dependence among over 35s
There is a general trend among humanity to first find a way to control something with technology, then to become dependent on that control. So we may find we have broken any natural systems which regulate the temperature on Earth, and our only option is to manage it ourselves via a series of technologies. Similarly, our lives increasingly depend on pharmaceuticals to keep us alive. It is conceivable, then, that a world where clever telomere-lengtheners are used widely by people in their 30s-40s; they could be an accepted medicine with a requirement that you continue to take them to keep topping up your telomeres, with perhaps a downside that you first have to disable a natural mechanism which would prevent it.
With the safety control removed, sudden loss of electronics via an EM pulse event would mean a sudden loss of the drugs to prolong life and an unavoidable tendency to get unstoppable cancer which is no longer controlled.
So: an EM arms race, universal telomere therapy, and then an incident
This seems like a reasonable point for a story; there are a few old people - either those who never took telomere therapy, or those who hide from the world to try to escape an HPV-like virus. Then a huge age gap of all the people who succumbed to the vagueries of a technological crutch being pulled away.
Presumably there would have been a huge global crisis as all the power structures of the old fell apart, all the technology stopped working. I would guess power, knowledge and skills would be handed down very suddenly to everyone under 30, and simultaneously a mass migration from the cities where populations are now concentrated to the countryside where the food is.
The skills to have would be metalwork, metal smelting; textbooks would be of huge value as the keys to a knowledge which rapidly fell away.