I'll second that this is a very good idea. See
here and
here for people performing well into their 70s and 80s, which just isn't accurate.
Problem is the traits should go down a little by the 40s, but there's no way for the game to know if the event's already fired. Might have a problem with someone getting run down to 0 pretty quickly.
And I'd think age would lower diplo (can't stay up all night, make as many trips, etc.) more than intrigue, which should rightly go up (or given game limitations, stay the same) with age unless the guy goes senile.
It would be sad, but appropriate, to have really debilitating senility events occasionally fire as well, on the order of the catatonic schizo one.