宝刀不老 Sharp blade never gets old
Explanation
这个成语比喻虽然年龄已大或脱离本行已久，但功夫技术并没减退。它可以用来形容人尽管年老，但依然精神矍铄，能力不减当年。
This idiom compares it to someone, although old or away from their profession for a long time, their skills and abilities have not diminished. It can be used to describe someone who, although old, still radiates and his abilities are not weaker than in his younger years.
Origin Story
三国时期，蜀国大将黄忠年事已高，但依然身手敏捷，作战勇猛。一次，在与魏国大将张郃的战斗中，张郃嘲讽黄忠年老，说他应该退隐在家，不要出来丢人现眼。黄忠却怒气冲冲地回应道：“竖子欺吾年老！吾手中宝刀却不老！”说完，他便挥舞着宝刀，冲锋陷阵，杀得魏军节节败退。黄忠宝刀不老，依然是蜀汉的顶梁柱，最终在与魏军的战斗中取得了胜利。
During the Three Kingdoms period, the Shu general Huang Zhong was already of advanced age, but was still agile and fought bravely. Once, in a battle against the Wei general Zhang He, Zhang He ridiculed Huang Zhong for his age, saying that he should retire at home and not go out to make a fool of himself. Huang Zhong, however, replied angrily: “You dare mock my old age! My blade is still sharp!” Then, he brandished his blade and charged into battle, driving the Wei army back step by step. Huang Zhong, still sharp as ever, was still a pillar of Shu Han, and ultimately won the battle against the Wei army.
Usage
这个成语主要用于形容人虽然年龄已大，但依然精神矍铄，能力不减当年，也可以用来比喻某项技术或技能依然精湛。
This idiom is mainly used to describe someone who, although old, still radiates and his abilities are not weaker than in his younger years. It can also be used to describe a particular technology or skill that is still excellent.
Examples
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老将军宝刀不老，仍然能够带领军队取得胜利。
lao jiang jun bao dao bu lao, reng ran neng gou dai ling jun dui qu de sheng li.
The old general is still fit and can lead the army to victory.
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虽然退休了，但老李宝刀不老，依然活跃在工作一线。
sui ran tui xiu le, dan lao li bao dao bu lao, yi ran huo yue zai gong zuo yi xian.
Although retired, Old Li is still fit and remains active on the front line of work.
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王老师宝刀不老，退休后还经常给学生们上课。
wang lao shi bao dao bu lao, tui xiu hou hai jing chang gei xue sheng men shang ke.
Professor Wang is still fit and often gives lectures to students after retirement.