Blood thinners and other potential medical conditions + thinning aging skin can lead to easy bruising. Around the hands and bonier areas (joints, shins, areas of less cushion) commonly bruise like this just from bumping into a hard surface.

I work with a hospice patient with liver cancer. Over the last couple months she's been developing bruises/purpura all over her body, some on the tops of her thighs just from resting a tray on her lap.