I've worked at procedural approach towers (app/aerodrome), international aerodrome control towers, area procedural and radar. Currently at a somewhat busy-ish international tower. I'm maybe a little over halfway through my career. (Depends on continuing to pass the medical.)
When I trained, the course was three years. A lot of "knowledge" was assimilated over that time, rather than the pressure cooker technique applied today. Part of the training was 60hrs flight training, with the PPL issue a requirement. I did another 500~ hours since then, for fun, on various (light) types, and learned a lot; had a lot of fun, and a few frights.
The lack of aviation training in ATC today is lamentable. I think it makes for a controller who is more likely to be confident in a wider range of situations.
I have no issue with todays trainees. Most of them are a hell of a lot sharper and smarter than I was (and am) and if I was ~20 again and applying, I doubt I'd get much past the second hurdle or thereabouts. They also have to work a lot harder to try and learn stuff in 6 months instead of three years, and that as much seems to stick as it does (in most cases) is, I feel, more a credit to the trainee than to the system that is producing them. I think that system owes them a much better quality of training than is often provided, from the selection process right on through, and including at least some flying training.