This is part of the issue - when you get very specific with magick you could block the manifestation of the outcome via other means, in this case it could keep him alive for longer.
I would say figure our what you really want - this person out of the way asap, or to play games with him first.
The first could happen by an accident, the 2nd ALSO requires you to do persuasion magick on unknown unnumbered other people, and do it as a relative beginner… it’s probably a non-starter. You can try I guess.
I suggest doing some divination to see what the outcomes look like and to look into what the protections are. A lot of baneful magick fails because it simply bounces off protections.
Look up “curse celebs” - we have a few threads about trying to do it. As far as I know, none of them came back saying it had worked.