Jason’s death was caused by his own impatience and inability to follow orders. Batman had repeatedly told Jason to not get involved and infact had grounded Jason from being Robin at one point. Jason repeatedly disobeyed orders, until at last his decision resulted him going into a situations alone that he wasn’t prepared for.

Tim’s father meanwhile wasn’t because of Batman or because of Tim’s age but because Tim had family. Jean Lorring hired Boomerang to targeted Tim because he was one of the few heroes who had proper family. Boomerang didn’t even know Tim was Robin and the fact Tim was Batman’s partner didn’t factor into anything. It was because Robin was a hero in his own right that he was a target.

As for Stephanie, again, she was 17 when she became Robin and then was “killed” shortly after. She was a legal adult who’d been acting as a vigilante for solo for a couple of years before. Her age and his grasp of reality doesn’t factor into things. Furthermore, she had been fired by Batman and ordered to give up being a hero. From that point forward the actions that led to her “death” were of her own actions and faulty decisions.

Dick was the only 10 year old sidekick he had. Jason Todd was 13 when Batman took him in. Tim Drake was 14 when he started his training, but was 15 when he was allowed to go into the field as Robin. Stephanie Brown was 17. And Damian Wayne meanwhile was selected by Dick Grayson to be Robin, not Bruce.