My grandfather is over seventy but still very robust.
Tips
history
From Du Fu's (杜甫) Tang-dynasty poem 《曲江》: 人生七十古来稀 - 'Reaching seventy has always been rare.' 古稀 (literally 'rare since ancient times') has since become a poetic name for the age of seventy.
register
Literary and respectful - used to refer to elderly people with dignity, especially in formal writing or biographical contexts. More elegant than just 七十多岁.
