There is scientific disagreement over impulsivity, and the distinction between impulsive and planning is so blurry as to be not that useful to a non-specialist. Also my quick skim of the topic was somewhat confusing because there is a different topic about whether impulsive personalities are more likely to suicide (probably not). And my case personally I am middle aged, and my peer group appears more likely to plan, which affects my anecdotal experience.
I think my problem is that the word “impulsive” is odd. Someone who has been thinking of committing suicide for months, and then one day “suddenly” decides to go through with it, seems to be considered by the literature to have made an impulsive decision. That definition doesn’t fit my usual meaning of the word impulsive (e.g. I don’t think it makes sense to say: I have been looking at cars to buy for two months and then I impulsively bought one).
Do you have a reason to imply most suicides are impulsive? I don’t think the media implies that (and my experience in New Zealand is they are not impulsive - usually following a long period of depression and maybe stated intent or attempts).