The age range from 70 to 79; someone in their seventies.
祖母は７０代だが、毎朝散歩を欠かさない。
My grandmother is in her seventies, but she never skips her morning walks.
７０代の人口割合が増えると医療や介護の需要が高まる。
As the proportion of people in their seventies increases, demand for medical care and nursing rises.
彼は７０代にして新しい楽器の演奏を始めた。
He started playing a new instrument in his seventies.