Coin Age is a measure of the number of years a coin has been held, and is used as a priority for Bitcoin trading and mining.
Coin Age is calculated by multiplying the amount of coins held by the length of time they have been held.
For example, if you hold 3BTC for 5 days, the Coin Age is 3 x 5 = 15BTC/day.
Coin Age is mainly used in mining called PoS (Proof of Stake). This is a method where the more coinage you hold, the more you can mine.
In cryptocurrencies that use the proof-of-stake system, the higher the Coin Age value, the more priority is given to mining.
Summary. Coin Age was introduced to improve the structure of stable transactions by eliminating the idea that those who hold the strongest electricity and computing power can be at the top of the transaction.