Originally Posted by
adkal
Although his abilities were 'played down' in his Post-COIE-youth: a bull trampled him when he was 8 years old and he didn't have a scratch on him, and he lifted a truck in order to get his ball. His vision (x-ray and telescopic) and hearing were also enhanced. It's more likely that this version of Superman (going with Byrne's psionic-approach to how Kal's abilities worked) held himself back in a way the previous versions never did (or could) and (later) only 'pushed' himself (a little) when competing against Kenny.
As for the question posed in the OP, I'm of the view that his mental abilities should kick in first, and as a newborn. Observing, processing, and adjusting - then, as the other abilities begin to develop and he's aware that we don't have them, he adapts accordingly.
As for other Kryptonians - my basic approach to them is that they get the abilities pretty much straight away, but it's temporary. Their cells soak up the juice and they get the powers, but it takes time for them to process and store the way Clark does, so that, in a matter of hours (depending on which abilities they indulge in and for how long) they come down to a base-level (GA) and it then takes them a couple of years (at least) of casual absorption to get back to being able to have heat vision.