While age is probably a factor in Italy, it's less of a factor in China, Iran and Spain, which also have high death rates (though the Chinese high death rate was mostly in the early stages). What these cases have in common is a very large surge which overwhelmed local health services.

If it was entirely based on age, you'd expect higher rates of death in Japan and Germany (both very elderly populations), lower in China (less elderly population) and much lower in Iran (young population).