taru-adjective, adverb taking the 'to' particle
vigorous in old age; hale and hearty
Describes an elderly person who is remarkably energetic and healthy. Often used in the phrase 矍鑠たる or adverbially with と.
祖父は90歳だが、まだかくしゃくとして毎日散歩している。
My grandfather is 90, but he is still hale and hearty and takes a walk every day.
あの老教授はかくしゃくたる足取りで教壇に立った。
The old professor stepped up to the podium with a vigorous gait.
The kanji 矍 and 鑠 both relate to brightness and vigor. The exact derivation is uncertain, but the compound is used to describe the lively appearance of an elderly person.