How is zakat paid on ancient coins that the questioner has owned since the age of fourteen, and does his current age play a role in the zakat?

Zakat (definition) is obligatory on ancient currencies if they are made of gold or silver and reach the nisab (definition) (85 grams of gold or 595 grams of silver), or its equivalent in banknotes. Zakat is to be paid on it every year at the rate of one-quarter of one-tenth (2.5%). As for currencies made of other metals, Zakat is not obligatory on them unless they are sold with the intention of trade and a hawl (one lunar year) passes on their price, which must reach the nisab. If they have no intrinsic value and are sold as an antique currency, it is not permissible to sell them, and the proceeds from their sale must be disposed of for public welfare. Zakat is obligatory on the wealth of a child, and their guardian must pay it.