How should one refer to somebody who wants to gain knowledge all the time and keeps learning in life even when very old?
What's the phrase for the same? My dictionary says "learn and live."
Sometimes there is no direct translation for a specific phrase. I have heard people use phrases like, "He is a life-long learner."
Lifelong learning is the obvious answer, but in case you need something more sophisticated, you could go for opsimathy.
"An opsimath is someone who begins, or continues, to study or learn late in life." (Ref: Wikipedia).