Theodore Roosevelt was 41 when McKinley was assassinated.
He was very accomplished at a young age – he had previously been the NYC police commissioner.
He had a hard life as well – he was blinded in one eye while boxing (when he was president).
He nearly died of a disease (I don’t remember which – malaria, sleeping sickness or something else) after his presidency whil on an adventurous tour.
He died when he was only 58 (I think).
He lost his son Quentin in WWI (Quentin Road in Brooklyn is named after the son).