Hi whereon my da didn't start to swim at a club until he was 12. He entered 50's and 100's because he was best at those and L3/4 meets did t often offer anything above that anyway.
His condition is degenerative so he also could do more at that younger age.
He wasn't classified until he was 17. He then started competing mainly in events for his classification and did 50m fee, 100m back, fly and free and 400m free.
It's only been this year he's pretty much dropped all but freestyle because he's not good at the other strokes really and because British para swimming g told him at british last year to work on his 400m free (which he focussed on 50/100 before that!)
He will do an odd back or fly if at club meet but he's not competing at these meets anymore. He's also done odd 800m free at meets as his coach said it's part of training for 400m!
Currently he's just racing 50/100/400m free but he's doing meets where he really needs to be on it for his target races and isn't competitive enough in the others to qualify to race them anyway!!!!!
At a younger age I would be doing all strokes and distances that are for their classification and a distance up to build the aerobic capacity but I'm not a coach so am just advising as a parent.