Instead of doing something like going around and fighting random thugs and criminals how about he joins a fighting class or something safe like that then go around beating innocent thugs.
To be fair, I don't think most people will actually know that they were going to die on that day if they were Jojo. Unless you actually know the date of their death, you don't really have a way to know. Sure, some people might say that they remembered the interactions between Tony and his parents before they left the house. But the sad thing is, this is already a different universe and things will be different, the interactions will be different with Jojo there. If you can't write emotional scenes where the characters tear up you should just rush past them or simplifie them to prevent any cringe worthy scenes in the future. And one last thing, you could make this as a starting point for the changes in the MC's personality ( since you can't really expect an Innocent and lovely child to be more prone to violence and fighting so suddenly , at least to Tony and the public) you should make him more delinquent like so that can be an excuse as to why he gets into fight a lot.
Is not better that he train I don't know some kind of martial arts before going to fight some random thugs, because is he use his powers he going to faint and then die
CaptainBoyHole