This term is similar to, if not absolutely synonymous with, "mature student". It is derived from two ancient Greek words, meaning simply "late" and "learn".

In previous times, it was used rather condescendingly, and as the proverb "You can't teach an old dog new tricks" proves, some doubted that it was even possible. But there have always been noteworthy opsimaths - a noteworthy ancient example being the Roman senator and historian Cato the Elder (234-149 BCE) who only learnt Greek when he was 80. Coming rather more up to date, Anna Mary Robertson Moses, known as "Grandma Moses" (1860-1961) only took up painting seriously in her late 70s. Even Queen Victoria (1819-1901) was known to have learnt Hindi when she was an old lady.

Fortunately, we now live in times when it is recognised that there is no upper age limit on learning, as is reflected in organisations like the Open University and the University of the Third Age.

More Info: en.wikipedia.org