What does the cryptic crossword clue "New moon Indian used to denote age (4,6)" mean?

The definition is "age". The wordplay uses an anagram. anagram of MOON + INDIAN = ANNODOMINI; definition: "age" The answer is ANNODOMINI.

New moon Indian used to denote age (4,6)

Guardian Cryptic #24752 | 14 Down | 2009-07-15 flower